FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_umtx.c

     /*-
      * Copyright (c) 2004, David Xu <davidxu@freebsd.org>
      * Copyright (c) 2002, Jeffrey Roberson <jeff@freebsd.org>
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
     *    notice unmodified, this list of conditions, and the following
     *    disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/9.1/sys/kern/kern_umtx.c 234505 2012-04-20 21:40:31Z davide $");
    
    #include "opt_compat.h"
    #include "opt_umtx_profiling.h"
    
    #include <sys/param.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mutex.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/sysent.h>
    #include <sys/systm.h>
    #include <sys/sysproto.h>
    #include <sys/syscallsubr.h>
    #include <sys/eventhandler.h>
    #include <sys/umtx.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_object.h>
    
    #include <machine/cpu.h>
    
    #ifdef COMPAT_FREEBSD32
    #include <compat/freebsd32/freebsd32_proto.h>
    #endif
    
    #define _UMUTEX_TRY             1
    #define _UMUTEX_WAIT            2
    
    /* Priority inheritance mutex info. */
    struct umtx_pi {
            /* Owner thread */
            struct thread           *pi_owner;
    
            /* Reference count */
            int                     pi_refcount;
    
            /* List entry to link umtx holding by thread */
            TAILQ_ENTRY(umtx_pi)    pi_link;
    
            /* List entry in hash */
            TAILQ_ENTRY(umtx_pi)    pi_hashlink;
    
            /* List for waiters */
            TAILQ_HEAD(,umtx_q)     pi_blocked;
    
            /* Identify a userland lock object */
            struct umtx_key         pi_key;
    };
    
    /* A userland synchronous object user. */
    struct umtx_q {
            /* Linked list for the hash. */
            TAILQ_ENTRY(umtx_q)     uq_link;
    
            /* Umtx key. */
            struct umtx_key         uq_key;
    
            /* Umtx flags. */
            int                     uq_flags;
    #define UQF_UMTXQ       0x0001
    
           /* The thread waits on. */
           struct thread           *uq_thread;
   
           /*
            * Blocked on PI mutex. read can use chain lock
            * or umtx_lock, write must have both chain lock and
            * umtx_lock being hold.
            */
           struct umtx_pi          *uq_pi_blocked;
   
           /* On blocked list */
           TAILQ_ENTRY(umtx_q)     uq_lockq;
   
           /* Thread contending with us */
           TAILQ_HEAD(,umtx_pi)    uq_pi_contested;
   
           /* Inherited priority from PP mutex */
           u_char                  uq_inherited_pri;
           
           /* Spare queue ready to be reused */
           struct umtxq_queue      *uq_spare_queue;
   
           /* The queue we on */
           struct umtxq_queue      *uq_cur_queue;
   };
   
   TAILQ_HEAD(umtxq_head, umtx_q);
   
   /* Per-key wait-queue */
   struct umtxq_queue {
           struct umtxq_head       head;
           struct umtx_key         key;
           LIST_ENTRY(umtxq_queue) link;
           int                     length;
   };
   
   LIST_HEAD(umtxq_list, umtxq_queue);
   
   /* Userland lock object's wait-queue chain */
   struct umtxq_chain {
           /* Lock for this chain. */
           struct mtx              uc_lock;
   
           /* List of sleep queues. */
           struct umtxq_list       uc_queue[2];
   #define UMTX_SHARED_QUEUE       0
   #define UMTX_EXCLUSIVE_QUEUE    1
   
           LIST_HEAD(, umtxq_queue) uc_spare_queue;
   
           /* Busy flag */
           char                    uc_busy;
   
           /* Chain lock waiters */
           int                     uc_waiters;
   
           /* All PI in the list */
           TAILQ_HEAD(,umtx_pi)    uc_pi_list;
   
   #ifdef UMTX_PROFILING
           int                     length;
           int                     max_length;
   #endif
   };
   
   #define UMTXQ_LOCKED_ASSERT(uc)         mtx_assert(&(uc)->uc_lock, MA_OWNED)
   #define UMTXQ_BUSY_ASSERT(uc)   KASSERT(&(uc)->uc_busy, ("umtx chain is not busy"))
   
   /*
    * Don't propagate time-sharing priority, there is a security reason,
    * a user can simply introduce PI-mutex, let thread A lock the mutex,
    * and let another thread B block on the mutex, because B is
    * sleeping, its priority will be boosted, this causes A's priority to
    * be boosted via priority propagating too and will never be lowered even
    * if it is using 100%CPU, this is unfair to other processes.
    */
   
   #define UPRI(td)        (((td)->td_user_pri >= PRI_MIN_TIMESHARE &&\
                             (td)->td_user_pri <= PRI_MAX_TIMESHARE) ?\
                            PRI_MAX_TIMESHARE : (td)->td_user_pri)
   
   #define GOLDEN_RATIO_PRIME      2654404609U
   #define UMTX_CHAINS             512
   #define UMTX_SHIFTS             (__WORD_BIT - 9)
   
   #define GET_SHARE(flags)        \
       (((flags) & USYNC_PROCESS_SHARED) == 0 ? THREAD_SHARE : PROCESS_SHARE)
   
   #define BUSY_SPINS              200
   
   static uma_zone_t               umtx_pi_zone;
   static struct umtxq_chain       umtxq_chains[2][UMTX_CHAINS];
   static MALLOC_DEFINE(M_UMTX, "umtx", "UMTX queue memory");
   static int                      umtx_pi_allocated;
   
   SYSCTL_NODE(_debug, OID_AUTO, umtx, CTLFLAG_RW, 0, "umtx debug");
   SYSCTL_INT(_debug_umtx, OID_AUTO, umtx_pi_allocated, CTLFLAG_RD,
       &umtx_pi_allocated, 0, "Allocated umtx_pi");
   
   #ifdef UMTX_PROFILING
   static long max_length;
   SYSCTL_LONG(_debug_umtx, OID_AUTO, max_length, CTLFLAG_RD, &max_length, 0, "max_length");
   static SYSCTL_NODE(_debug_umtx, OID_AUTO, chains, CTLFLAG_RD, 0, "umtx chain stats");
   #endif
   
   static void umtxq_sysinit(void *);
   static void umtxq_hash(struct umtx_key *key);
   static struct umtxq_chain *umtxq_getchain(struct umtx_key *key);
   static void umtxq_lock(struct umtx_key *key);
   static void umtxq_unlock(struct umtx_key *key);
   static void umtxq_busy(struct umtx_key *key);
   static void umtxq_unbusy(struct umtx_key *key);
   static void umtxq_insert_queue(struct umtx_q *uq, int q);
   static void umtxq_remove_queue(struct umtx_q *uq, int q);
   static int umtxq_sleep(struct umtx_q *uq, const char *wmesg, int timo);
   static int umtxq_count(struct umtx_key *key);
   static struct umtx_pi *umtx_pi_alloc(int);
   static void umtx_pi_free(struct umtx_pi *pi);
   static int do_unlock_pp(struct thread *td, struct umutex *m, uint32_t flags);
   static void umtx_thread_cleanup(struct thread *td);
   static void umtx_exec_hook(void *arg __unused, struct proc *p __unused,
           struct image_params *imgp __unused);
   SYSINIT(umtx, SI_SUB_EVENTHANDLER+1, SI_ORDER_MIDDLE, umtxq_sysinit, NULL);
   
   #define umtxq_signal(key, nwake)        umtxq_signal_queue((key), (nwake), UMTX_SHARED_QUEUE)
   #define umtxq_insert(uq)        umtxq_insert_queue((uq), UMTX_SHARED_QUEUE)
   #define umtxq_remove(uq)        umtxq_remove_queue((uq), UMTX_SHARED_QUEUE)
   
   static struct mtx umtx_lock;
   
   #ifdef UMTX_PROFILING
   static void
   umtx_init_profiling(void) 
   {
           struct sysctl_oid *chain_oid;
           char chain_name[10];
           int i;
   
           for (i = 0; i < UMTX_CHAINS; ++i) {
                   snprintf(chain_name, sizeof(chain_name), "%d", i);
                   chain_oid = SYSCTL_ADD_NODE(NULL, 
                       SYSCTL_STATIC_CHILDREN(_debug_umtx_chains), OID_AUTO, 
                       chain_name, CTLFLAG_RD, NULL, "umtx hash stats");
                   SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
                       "max_length0", CTLFLAG_RD, &umtxq_chains[0][i].max_length, 0, NULL);
                   SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
                       "max_length1", CTLFLAG_RD, &umtxq_chains[1][i].max_length, 0, NULL);
           }
   }
   #endif
   
   static void
   umtxq_sysinit(void *arg __unused)
   {
           int i, j;
   
           umtx_pi_zone = uma_zcreate("umtx pi", sizeof(struct umtx_pi),
                   NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
           for (i = 0; i < 2; ++i) {
                   for (j = 0; j < UMTX_CHAINS; ++j) {
                           mtx_init(&umtxq_chains[i][j].uc_lock, "umtxql", NULL,
                                    MTX_DEF | MTX_DUPOK);
                           LIST_INIT(&umtxq_chains[i][j].uc_queue[0]);
                           LIST_INIT(&umtxq_chains[i][j].uc_queue[1]);
                           LIST_INIT(&umtxq_chains[i][j].uc_spare_queue);
                           TAILQ_INIT(&umtxq_chains[i][j].uc_pi_list);
                           umtxq_chains[i][j].uc_busy = 0;
                           umtxq_chains[i][j].uc_waiters = 0;
   #ifdef UMTX_PROFILING
                           umtxq_chains[i][j].length = 0;
                           umtxq_chains[i][j].max_length = 0;      
   #endif
                   }
           }
   #ifdef UMTX_PROFILING
           umtx_init_profiling();
   #endif
           mtx_init(&umtx_lock, "umtx lock", NULL, MTX_SPIN);
           EVENTHANDLER_REGISTER(process_exec, umtx_exec_hook, NULL,
               EVENTHANDLER_PRI_ANY);
   }
   
   struct umtx_q *
   umtxq_alloc(void)
   {
           struct umtx_q *uq;
   
           uq = malloc(sizeof(struct umtx_q), M_UMTX, M_WAITOK | M_ZERO);
           uq->uq_spare_queue = malloc(sizeof(struct umtxq_queue), M_UMTX, M_WAITOK | M_ZERO);
           TAILQ_INIT(&uq->uq_spare_queue->head);
           TAILQ_INIT(&uq->uq_pi_contested);
           uq->uq_inherited_pri = PRI_MAX;
           return (uq);
   }
   
   void
   umtxq_free(struct umtx_q *uq)
   {
           MPASS(uq->uq_spare_queue != NULL);
           free(uq->uq_spare_queue, M_UMTX);
           free(uq, M_UMTX);
   }
   
   static inline void
   umtxq_hash(struct umtx_key *key)
   {
           unsigned n = (uintptr_t)key->info.both.a + key->info.both.b;
           key->hash = ((n * GOLDEN_RATIO_PRIME) >> UMTX_SHIFTS) % UMTX_CHAINS;
   }
   
   static inline struct umtxq_chain *
   umtxq_getchain(struct umtx_key *key)
   {
           if (key->type <= TYPE_SEM)
                   return (&umtxq_chains[1][key->hash]);
           return (&umtxq_chains[0][key->hash]);
   }
   
   /*
    * Lock a chain.
    */
   static inline void
   umtxq_lock(struct umtx_key *key)
   {
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(key);
           mtx_lock(&uc->uc_lock);
   }
   
   /*
    * Unlock a chain.
    */
   static inline void
   umtxq_unlock(struct umtx_key *key)
   {
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(key);
           mtx_unlock(&uc->uc_lock);
   }
   
   /*
    * Set chain to busy state when following operation
    * may be blocked (kernel mutex can not be used).
    */
   static inline void
   umtxq_busy(struct umtx_key *key)
   {
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(key);
           mtx_assert(&uc->uc_lock, MA_OWNED);
           if (uc->uc_busy) {
   #ifdef SMP
                   if (smp_cpus > 1) {
                           int count = BUSY_SPINS;
                           if (count > 0) {
                                   umtxq_unlock(key);
                                   while (uc->uc_busy && --count > 0)
                                           cpu_spinwait();
                                   umtxq_lock(key);
                           }
                   }
   #endif
                   while (uc->uc_busy) {
                           uc->uc_waiters++;
                           msleep(uc, &uc->uc_lock, 0, "umtxqb", 0);
                           uc->uc_waiters--;
                   }
           }
           uc->uc_busy = 1;
   }
   
   /*
    * Unbusy a chain.
    */
   static inline void
   umtxq_unbusy(struct umtx_key *key)
   {
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(key);
           mtx_assert(&uc->uc_lock, MA_OWNED);
           KASSERT(uc->uc_busy != 0, ("not busy"));
           uc->uc_busy = 0;
           if (uc->uc_waiters)
                   wakeup_one(uc);
   }
   
   static struct umtxq_queue *
   umtxq_queue_lookup(struct umtx_key *key, int q)
   {
           struct umtxq_queue *uh;
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(key);
           UMTXQ_LOCKED_ASSERT(uc);
           LIST_FOREACH(uh, &uc->uc_queue[q], link) {
                   if (umtx_key_match(&uh->key, key))
                           return (uh);
           }
   
           return (NULL);
   }
   
   static inline void
   umtxq_insert_queue(struct umtx_q *uq, int q)
   {
           struct umtxq_queue *uh;
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(&uq->uq_key);
           UMTXQ_LOCKED_ASSERT(uc);
           KASSERT((uq->uq_flags & UQF_UMTXQ) == 0, ("umtx_q is already on queue"));
           uh = umtxq_queue_lookup(&uq->uq_key, q);
           if (uh != NULL) {
                   LIST_INSERT_HEAD(&uc->uc_spare_queue, uq->uq_spare_queue, link);
           } else {
                   uh = uq->uq_spare_queue;
                   uh->key = uq->uq_key;
                   LIST_INSERT_HEAD(&uc->uc_queue[q], uh, link);
           }
           uq->uq_spare_queue = NULL;
   
           TAILQ_INSERT_TAIL(&uh->head, uq, uq_link);
           uh->length++;
   #ifdef UMTX_PROFILING
           uc->length++;
           if (uc->length > uc->max_length) {
                   uc->max_length = uc->length;
                   if (uc->max_length > max_length)
                           max_length = uc->max_length;    
           }
   #endif
           uq->uq_flags |= UQF_UMTXQ;
           uq->uq_cur_queue = uh;
           return;
   }
   
   static inline void
   umtxq_remove_queue(struct umtx_q *uq, int q)
   {
           struct umtxq_chain *uc;
           struct umtxq_queue *uh;
   
           uc = umtxq_getchain(&uq->uq_key);
           UMTXQ_LOCKED_ASSERT(uc);
           if (uq->uq_flags & UQF_UMTXQ) {
                   uh = uq->uq_cur_queue;
                   TAILQ_REMOVE(&uh->head, uq, uq_link);
                   uh->length--;
   #ifdef UMTX_PROFILING
                   uc->length--;
   #endif
                   uq->uq_flags &= ~UQF_UMTXQ;
                   if (TAILQ_EMPTY(&uh->head)) {
                           KASSERT(uh->length == 0,
                               ("inconsistent umtxq_queue length"));
                           LIST_REMOVE(uh, link);
                   } else {
                           uh = LIST_FIRST(&uc->uc_spare_queue);
                           KASSERT(uh != NULL, ("uc_spare_queue is empty"));
                           LIST_REMOVE(uh, link);
                   }
                   uq->uq_spare_queue = uh;
                   uq->uq_cur_queue = NULL;
           }
   }
   
   /*
    * Check if there are multiple waiters
    */
   static int
   umtxq_count(struct umtx_key *key)
   {
           struct umtxq_chain *uc;
           struct umtxq_queue *uh;
   
           uc = umtxq_getchain(key);
           UMTXQ_LOCKED_ASSERT(uc);
           uh = umtxq_queue_lookup(key, UMTX_SHARED_QUEUE);
           if (uh != NULL)
                   return (uh->length);
           return (0);
   }
   
   /*
    * Check if there are multiple PI waiters and returns first
    * waiter.
    */
   static int
   umtxq_count_pi(struct umtx_key *key, struct umtx_q **first)
   {
           struct umtxq_chain *uc;
           struct umtxq_queue *uh;
   
           *first = NULL;
           uc = umtxq_getchain(key);
           UMTXQ_LOCKED_ASSERT(uc);
           uh = umtxq_queue_lookup(key, UMTX_SHARED_QUEUE);
           if (uh != NULL) {
                   *first = TAILQ_FIRST(&uh->head);
                   return (uh->length);
           }
           return (0);
   }
   
   /*
    * Wake up threads waiting on an userland object.
    */
   
   static int
   umtxq_signal_queue(struct umtx_key *key, int n_wake, int q)
   {
           struct umtxq_chain *uc;
           struct umtxq_queue *uh;
           struct umtx_q *uq;
           int ret;
   
           ret = 0;
           uc = umtxq_getchain(key);
           UMTXQ_LOCKED_ASSERT(uc);
           uh = umtxq_queue_lookup(key, q);
           if (uh != NULL) {
                   while ((uq = TAILQ_FIRST(&uh->head)) != NULL) {
                           umtxq_remove_queue(uq, q);
                           wakeup(uq);
                           if (++ret >= n_wake)
                                   return (ret);
                   }
           }
           return (ret);
   }
   
   
   /*
    * Wake up specified thread.
    */
   static inline void
   umtxq_signal_thread(struct umtx_q *uq)
   {
           struct umtxq_chain *uc;
   
           uc = umtxq_getchain(&uq->uq_key);
           UMTXQ_LOCKED_ASSERT(uc);
           umtxq_remove(uq);
           wakeup(uq);
   }
   
   /*
    * Put thread into sleep state, before sleeping, check if
    * thread was removed from umtx queue.
    */
   static inline int
   umtxq_sleep(struct umtx_q *uq, const char *wmesg, int timo)
   {
           struct umtxq_chain *uc;
           int error;
   
           uc = umtxq_getchain(&uq->uq_key);
           UMTXQ_LOCKED_ASSERT(uc);
           if (!(uq->uq_flags & UQF_UMTXQ))
                   return (0);
           error = msleep(uq, &uc->uc_lock, PCATCH, wmesg, timo);
           if (error == EWOULDBLOCK)
                   error = ETIMEDOUT;
           return (error);
   }
   
   /*
    * Convert userspace address into unique logical address.
    */
   int
   umtx_key_get(void *addr, int type, int share, struct umtx_key *key)
   {
           struct thread *td = curthread;
           vm_map_t map;
           vm_map_entry_t entry;
           vm_pindex_t pindex;
           vm_prot_t prot;
           boolean_t wired;
   
           key->type = type;
           if (share == THREAD_SHARE) {
                   key->shared = 0;
                   key->info.private.vs = td->td_proc->p_vmspace;
                   key->info.private.addr = (uintptr_t)addr;
           } else {
                   MPASS(share == PROCESS_SHARE || share == AUTO_SHARE);
                   map = &td->td_proc->p_vmspace->vm_map;
                   if (vm_map_lookup(&map, (vm_offset_t)addr, VM_PROT_WRITE,
                       &entry, &key->info.shared.object, &pindex, &prot,
                       &wired) != KERN_SUCCESS) {
                           return EFAULT;
                   }
   
                   if ((share == PROCESS_SHARE) ||
                       (share == AUTO_SHARE &&
                        VM_INHERIT_SHARE == entry->inheritance)) {
                           key->shared = 1;
                           key->info.shared.offset = entry->offset + entry->start -
                                   (vm_offset_t)addr;
                           vm_object_reference(key->info.shared.object);
                   } else {
                           key->shared = 0;
                           key->info.private.vs = td->td_proc->p_vmspace;
                           key->info.private.addr = (uintptr_t)addr;
                   }
                   vm_map_lookup_done(map, entry);
           }
   
           umtxq_hash(key);
           return (0);
   }
   
   /*
    * Release key.
    */
   void
   umtx_key_release(struct umtx_key *key)
   {
           if (key->shared)
                   vm_object_deallocate(key->info.shared.object);
   }
   
   /*
    * Lock a umtx object.
    */
   static int
   _do_lock_umtx(struct thread *td, struct umtx *umtx, u_long id, int timo)
   {
           struct umtx_q *uq;
           u_long owner;
           u_long old;
           int error = 0;
   
           uq = td->td_umtxq;
   
           /*
            * Care must be exercised when dealing with umtx structure. It
            * can fault on any access.
            */
           for (;;) {
                   /*
                    * Try the uncontested case.  This should be done in userland.
                    */
                   owner = casuword(&umtx->u_owner, UMTX_UNOWNED, id);
   
                   /* The acquire succeeded. */
                   if (owner == UMTX_UNOWNED)
                           return (0);
   
                   /* The address was invalid. */
                   if (owner == -1)
                           return (EFAULT);
   
                   /* If no one owns it but it is contested try to acquire it. */
                   if (owner == UMTX_CONTESTED) {
                           owner = casuword(&umtx->u_owner,
                               UMTX_CONTESTED, id | UMTX_CONTESTED);
   
                           if (owner == UMTX_CONTESTED)
                                   return (0);
   
                           /* The address was invalid. */
                           if (owner == -1)
                                   return (EFAULT);
   
                           /* If this failed the lock has changed, restart. */
                           continue;
                   }
   
                   /*
                    * If we caught a signal, we have retried and now
                    * exit immediately.
                    */
                   if (error != 0)
                           return (error);
   
                   if ((error = umtx_key_get(umtx, TYPE_SIMPLE_LOCK,
                           AUTO_SHARE, &uq->uq_key)) != 0)
                           return (error);
   
                   umtxq_lock(&uq->uq_key);
                   umtxq_busy(&uq->uq_key);
                   umtxq_insert(uq);
                   umtxq_unbusy(&uq->uq_key);
                   umtxq_unlock(&uq->uq_key);
   
                   /*
                    * Set the contested bit so that a release in user space
                    * knows to use the system call for unlock.  If this fails
                    * either some one else has acquired the lock or it has been
                    * released.
                    */
                   old = casuword(&umtx->u_owner, owner, owner | UMTX_CONTESTED);
   
                   /* The address was invalid. */
                   if (old == -1) {
                           umtxq_lock(&uq->uq_key);
                           umtxq_remove(uq);
                           umtxq_unlock(&uq->uq_key);
                           umtx_key_release(&uq->uq_key);
                           return (EFAULT);
                   }
   
                   /*
                    * We set the contested bit, sleep. Otherwise the lock changed
                    * and we need to retry or we lost a race to the thread
                    * unlocking the umtx.
                    */
                   umtxq_lock(&uq->uq_key);
                   if (old == owner)
                           error = umtxq_sleep(uq, "umtx", timo);
                   umtxq_remove(uq);
                   umtxq_unlock(&uq->uq_key);
                   umtx_key_release(&uq->uq_key);
           }
   
           return (0);
   }
   
   /*
    * Lock a umtx object.
    */
   static int
   do_lock_umtx(struct thread *td, struct umtx *umtx, u_long id,
           struct timespec *timeout)
   {
           struct timespec ts, ts2, ts3;
           struct timeval tv;
           int error;
   
           if (timeout == NULL) {
                   error = _do_lock_umtx(td, umtx, id, 0);
                   /* Mutex locking is restarted if it is interrupted. */
                   if (error == EINTR)
                           error = ERESTART;
           } else {
                   getnanouptime(&ts);
                   timespecadd(&ts, timeout);
                   TIMESPEC_TO_TIMEVAL(&tv, timeout);
                   for (;;) {
                           error = _do_lock_umtx(td, umtx, id, tvtohz(&tv));
                           if (error != ETIMEDOUT)
                                   break;
                           getnanouptime(&ts2);
                           if (timespeccmp(&ts2, &ts, >=)) {
                                   error = ETIMEDOUT;
                                   break;
                           }
                           ts3 = ts;
                           timespecsub(&ts3, &ts2);
                           TIMESPEC_TO_TIMEVAL(&tv, &ts3);
                   }
                   /* Timed-locking is not restarted. */
                   if (error == ERESTART)
                           error = EINTR;
           }
           return (error);
   }
   
   /*
    * Unlock a umtx object.
    */
   static int
   do_unlock_umtx(struct thread *td, struct umtx *umtx, u_long id)
   {
           struct umtx_key key;
           u_long owner;
           u_long old;
           int error;
           int count;
   
           /*
            * Make sure we own this mtx.
            */
           owner = fuword(__DEVOLATILE(u_long *, &umtx->u_owner));
           if (owner == -1)
                   return (EFAULT);
   
           if ((owner & ~UMTX_CONTESTED) != id)
                   return (EPERM);
   
           /* This should be done in userland */
           if ((owner & UMTX_CONTESTED) == 0) {
                   old = casuword(&umtx->u_owner, owner, UMTX_UNOWNED);
                   if (old == -1)
                           return (EFAULT);
                   if (old == owner)
                           return (0);
                   owner = old;
           }
   
           /* We should only ever be in here for contested locks */
           if ((error = umtx_key_get(umtx, TYPE_SIMPLE_LOCK, AUTO_SHARE,
                   &key)) != 0)
                   return (error);
   
           umtxq_lock(&key);
           umtxq_busy(&key);
           count = umtxq_count(&key);
           umtxq_unlock(&key);
   
           /*
            * When unlocking the umtx, it must be marked as unowned if
            * there is zero or one thread only waiting for it.
            * Otherwise, it must be marked as contested.
            */
           old = casuword(&umtx->u_owner, owner,
                   count <= 1 ? UMTX_UNOWNED : UMTX_CONTESTED);
           umtxq_lock(&key);
           umtxq_signal(&key,1);
           umtxq_unbusy(&key);
           umtxq_unlock(&key);
           umtx_key_release(&key);
           if (old == -1)
                   return (EFAULT);
           if (old != owner)
                   return (EINVAL);
           return (0);
   }
   
   #ifdef COMPAT_FREEBSD32
   
   /*
    * Lock a umtx object.
    */
   static int
   _do_lock_umtx32(struct thread *td, uint32_t *m, uint32_t id, int timo)
   {
           struct umtx_q *uq;
           uint32_t owner;
           uint32_t old;
           int error = 0;
   
           uq = td->td_umtxq;
   
           /*
            * Care must be exercised when dealing with umtx structure. It
            * can fault on any access.
            */
           for (;;) {
                   /*
                    * Try the uncontested case.  This should be done in userland.
                    */
                   owner = casuword32(m, UMUTEX_UNOWNED, id);
   
                   /* The acquire succeeded. */
                   if (owner == UMUTEX_UNOWNED)
                           return (0);
   
                   /* The address was invalid. */
                   if (owner == -1)
                           return (EFAULT);
   
                   /* If no one owns it but it is contested try to acquire it. */
                   if (owner == UMUTEX_CONTESTED) {
                           owner = casuword32(m,
                               UMUTEX_CONTESTED, id | UMUTEX_CONTESTED);
                           if (owner == UMUTEX_CONTESTED)
                                   return (0);
   
                           /* The address was invalid. */
                           if (owner == -1)
                                   return (EFAULT);
   
                           /* If this failed the lock has changed, restart. */
                           continue;
                   }
   
                   /*
                    * If we caught a signal, we have retried and now
                    * exit immediately.
                    */
                   if (error != 0)
                           return (error);
   
                   if ((error = umtx_key_get(m, TYPE_SIMPLE_LOCK,
                           AUTO_SHARE, &uq->uq_key)) != 0)
                           return (error);
   
                   umtxq_lock(&uq->uq_key);
                   umtxq_busy(&uq->uq_key);
                   umtxq_insert(uq);
                   umtxq_unbusy(&uq->uq_key);
                   umtxq_unlock(&uq->uq_key);
   
                   /*
                    * Set the contested bit so that a release in user space
                    * knows to use the system call for unlock.  If this fails
                    * either some one else has acquired the lock or it has been
                    * released.
                    */
                   old = casuword32(m, owner, owner | UMUTEX_CONTESTED);
   
                   /* The address was invalid. */
                   if (old == -1) {
                           umtxq_lock(&uq->uq_key);
                           umtxq_remove(uq);
                           umtxq_unlock(&uq->uq_key);
                           umtx_key_release(&uq->uq_key);
                           return (EFAULT);
                   }
   
                   /*
                    * We set the contested bit, sleep. Otherwise the lock changed
                    * and we need to retry or we lost a race to the thread
                    * unlocking the umtx.
                    */
                   umtxq_lock(&uq->uq_key);
                   if (old == owner)
                           error = umtxq_sleep(uq, "umtx", timo);
                   umtxq_remove(uq);
                   umtxq_unlock(&uq->uq_key);
                   umtx_key_release(&uq->uq_key);
           }
   
           return (0);
   }
   
   /*
    * Lock a umtx object.
    */
   static int
   do_lock_umtx32(struct thread *td, void *m, uint32_t id,
           struct timespec *timeout)
   {
           struct timespec ts, ts2, ts3;
           struct timeval tv;
           int error;
   
           if (timeout == NULL) {
                   error = _do_lock_umtx32(td, m, id, 0);
                   /* Mutex locking is restarted if it is interrupted. */
                   if (error == EINTR)
                           error = ERESTART;
           } else {
                   getnanouptime(&ts);
                   timespecadd(&ts, timeout);
                   TIMESPEC_TO_TIMEVAL(&tv, timeout);
                   for (;;) {
                           error = _do_lock_umtx32(td, m, id, tvtohz(&tv));
                           if (error != ETIMEDOUT)
                                   break;
                           getnanouptime(&ts2);
                           if (timespeccmp(&ts2, &ts, >=)) {
                                   error = ETIMEDOUT;
                                   break;
                           }
                           ts3 = ts;
                           timespecsub(&ts3, &ts2);
                           TIMESPEC_TO_TIMEVAL(&tv, &ts3);
                   }
                   /* Timed-locking is not restarted. */
                   if (error == ERESTART)
                           error = EINTR;
           }
           return (error);
   }
   
   /*
    * Unlock a umtx object.
    */
   static int
   do_unlock_umtx32(struct thread *td, uint32_t *m, uint32_t id)
   {
           struct umtx_key key;
           uint32_t owner;
           uint32_t old;
           int error;
           int count;
   
           /*
            * Make sure we own this mtx.
            */
           owner = fuword32(m);
           if (owner == -1)
                   return (EFAULT);
   
           if ((owner & ~UMUTEX_CONTESTED) != id)
                   return (EPERM);
   
           /* This should be done in userland */
           if ((owner & UMUTEX_CONTESTED) == 0) {
                   old = casuword32(m, owner, UMUTEX_UNOWNED);
                   if (old == -1)
                           return (EFAULT);
                   if (old == owner)
                           return (0);
                   owner = old;
           }
   
           /* We should only ever be in here for contested locks */
           if ((error = umtx_key_get(m, TYPE_SIMPLE_LOCK, AUTO_SHARE,
                   &key)) != 0)
                   return (error);
   
           umtxq_lock(&key);
          umtxq_busy(&key);
          count = umtxq_count(&key);
          umtxq_unlock(&key);
  
          /*
           * When unlocking the umtx, it must be marked as unowned if
           * there is zero or one thread only waiting for it.
           * Otherwise, it must be marked as contested.
           */
          old = casuword32(m, owner,
                  count <= 1 ? UMUTEX_UNOWNED : UMUTEX_CONTESTED);
          umtxq_lock(&key);
          umtxq_signal(&key,1);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          if (old == -1)
                  return (EFAULT);
          if (old != owner)
                  return (EINVAL);
          return (0);
  }
  #endif
  
  /*
   * Fetch and compare value, sleep on the address if value is not changed.
   */
  static int
  do_wait(struct thread *td, void *addr, u_long id,
          struct timespec *timeout, int compat32, int is_private)
  {
          struct umtx_q *uq;
          struct timespec ts, ts2, ts3;
          struct timeval tv;
          u_long tmp;
          int error = 0;
  
          uq = td->td_umtxq;
          if ((error = umtx_key_get(addr, TYPE_SIMPLE_WAIT,
                  is_private ? THREAD_SHARE : AUTO_SHARE, &uq->uq_key)) != 0)
                  return (error);
  
          umtxq_lock(&uq->uq_key);
          umtxq_insert(uq);
          umtxq_unlock(&uq->uq_key);
          if (compat32 == 0)
                  tmp = fuword(addr);
          else
                  tmp = (unsigned int)fuword32(addr);
          if (tmp != id) {
                  umtxq_lock(&uq->uq_key);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
          } else if (timeout == NULL) {
                  umtxq_lock(&uq->uq_key);
                  error = umtxq_sleep(uq, "uwait", 0);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
          } else {
                  getnanouptime(&ts);
                  timespecadd(&ts, timeout);
                  TIMESPEC_TO_TIMEVAL(&tv, timeout);
                  umtxq_lock(&uq->uq_key);
                  for (;;) {
                          error = umtxq_sleep(uq, "uwait", tvtohz(&tv));
                          if (!(uq->uq_flags & UQF_UMTXQ)) {
                                  error = 0;
                                  break;
                          }
                          if (error != ETIMEDOUT)
                                  break;
                          umtxq_unlock(&uq->uq_key);
                          getnanouptime(&ts2);
                          if (timespeccmp(&ts2, &ts, >=)) {
                                  error = ETIMEDOUT;
                                  umtxq_lock(&uq->uq_key);
                                  break;
                          }
                          ts3 = ts;
                          timespecsub(&ts3, &ts2);
                          TIMESPEC_TO_TIMEVAL(&tv, &ts3);
                          umtxq_lock(&uq->uq_key);
                  }
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
          }
          umtx_key_release(&uq->uq_key);
          if (error == ERESTART)
                  error = EINTR;
          return (error);
  }
  
  /*
   * Wake up threads sleeping on the specified address.
   */
  int
  kern_umtx_wake(struct thread *td, void *uaddr, int n_wake, int is_private)
  {
          struct umtx_key key;
          int ret;
          
          if ((ret = umtx_key_get(uaddr, TYPE_SIMPLE_WAIT,
                  is_private ? THREAD_SHARE : AUTO_SHARE, &key)) != 0)
                  return (ret);
          umtxq_lock(&key);
          ret = umtxq_signal(&key, n_wake);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          return (0);
  }
  
  /*
   * Lock PTHREAD_PRIO_NONE protocol POSIX mutex.
   */
  static int
  _do_lock_normal(struct thread *td, struct umutex *m, uint32_t flags, int timo,
          int mode)
  {
          struct umtx_q *uq;
          uint32_t owner, old, id;
          int error = 0;
  
          id = td->td_tid;
          uq = td->td_umtxq;
  
          /*
           * Care must be exercised when dealing with umtx structure. It
           * can fault on any access.
           */
          for (;;) {
                  owner = fuword32(__DEVOLATILE(void *, &m->m_owner));
                  if (mode == _UMUTEX_WAIT) {
                          if (owner == UMUTEX_UNOWNED || owner == UMUTEX_CONTESTED)
                                  return (0);
                  } else {
                          /*
                           * Try the uncontested case.  This should be done in userland.
                           */
                          owner = casuword32(&m->m_owner, UMUTEX_UNOWNED, id);
  
                          /* The acquire succeeded. */
                          if (owner == UMUTEX_UNOWNED)
                                  return (0);
  
                          /* The address was invalid. */
                          if (owner == -1)
                                  return (EFAULT);
  
                          /* If no one owns it but it is contested try to acquire it. */
                          if (owner == UMUTEX_CONTESTED) {
                                  owner = casuword32(&m->m_owner,
                                      UMUTEX_CONTESTED, id | UMUTEX_CONTESTED);
  
                                  if (owner == UMUTEX_CONTESTED)
                                          return (0);
  
                                  /* The address was invalid. */
                                  if (owner == -1)
                                          return (EFAULT);
  
                                  /* If this failed the lock has changed, restart. */
                                  continue;
                          }
                  }
  
                  if ((flags & UMUTEX_ERROR_CHECK) != 0 &&
                      (owner & ~UMUTEX_CONTESTED) == id)
                          return (EDEADLK);
  
                  if (mode == _UMUTEX_TRY)
                          return (EBUSY);
  
                  /*
                   * If we caught a signal, we have retried and now
                   * exit immediately.
                   */
                  if (error != 0)
                          return (error);
  
                  if ((error = umtx_key_get(m, TYPE_NORMAL_UMUTEX,
                      GET_SHARE(flags), &uq->uq_key)) != 0)
                          return (error);
  
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_insert(uq);
                  umtxq_unlock(&uq->uq_key);
  
                  /*
                   * Set the contested bit so that a release in user space
                   * knows to use the system call for unlock.  If this fails
                   * either some one else has acquired the lock or it has been
                   * released.
                   */
                  old = casuword32(&m->m_owner, owner, owner | UMUTEX_CONTESTED);
  
                  /* The address was invalid. */
                  if (old == -1) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_remove(uq);
                          umtxq_unbusy(&uq->uq_key);
                          umtxq_unlock(&uq->uq_key);
                          umtx_key_release(&uq->uq_key);
                          return (EFAULT);
                  }
  
                  /*
                   * We set the contested bit, sleep. Otherwise the lock changed
                   * and we need to retry or we lost a race to the thread
                   * unlocking the umtx.
                   */
                  umtxq_lock(&uq->uq_key);
                  umtxq_unbusy(&uq->uq_key);
                  if (old == owner)
                          error = umtxq_sleep(uq, "umtxn", timo);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
                  umtx_key_release(&uq->uq_key);
          }
  
          return (0);
  }
  
  /*
   * Lock PTHREAD_PRIO_NONE protocol POSIX mutex.
   */
  /*
   * Unlock PTHREAD_PRIO_NONE protocol POSIX mutex.
   */
  static int
  do_unlock_normal(struct thread *td, struct umutex *m, uint32_t flags)
  {
          struct umtx_key key;
          uint32_t owner, old, id;
          int error;
          int count;
  
          id = td->td_tid;
          /*
           * Make sure we own this mtx.
           */
          owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
          if (owner == -1)
                  return (EFAULT);
  
          if ((owner & ~UMUTEX_CONTESTED) != id)
                  return (EPERM);
  
          if ((owner & UMUTEX_CONTESTED) == 0) {
                  old = casuword32(&m->m_owner, owner, UMUTEX_UNOWNED);
                  if (old == -1)
                          return (EFAULT);
                  if (old == owner)
                          return (0);
                  owner = old;
          }
  
          /* We should only ever be in here for contested locks */
          if ((error = umtx_key_get(m, TYPE_NORMAL_UMUTEX, GET_SHARE(flags),
              &key)) != 0)
                  return (error);
  
          umtxq_lock(&key);
          umtxq_busy(&key);
          count = umtxq_count(&key);
          umtxq_unlock(&key);
  
          /*
           * When unlocking the umtx, it must be marked as unowned if
           * there is zero or one thread only waiting for it.
           * Otherwise, it must be marked as contested.
           */
          old = casuword32(&m->m_owner, owner,
                  count <= 1 ? UMUTEX_UNOWNED : UMUTEX_CONTESTED);
          umtxq_lock(&key);
          umtxq_signal(&key,1);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          if (old == -1)
                  return (EFAULT);
          if (old != owner)
                  return (EINVAL);
          return (0);
  }
  
  /*
   * Check if the mutex is available and wake up a waiter,
   * only for simple mutex.
   */
  static int
  do_wake_umutex(struct thread *td, struct umutex *m)
  {
          struct umtx_key key;
          uint32_t owner;
          uint32_t flags;
          int error;
          int count;
  
          owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
          if (owner == -1)
                  return (EFAULT);
  
          if ((owner & ~UMUTEX_CONTESTED) != 0)
                  return (0);
  
          flags = fuword32(&m->m_flags);
  
          /* We should only ever be in here for contested locks */
          if ((error = umtx_key_get(m, TYPE_NORMAL_UMUTEX, GET_SHARE(flags),
              &key)) != 0)
                  return (error);
  
          umtxq_lock(&key);
          umtxq_busy(&key);
          count = umtxq_count(&key);
          umtxq_unlock(&key);
  
          if (count <= 1)
                  owner = casuword32(&m->m_owner, UMUTEX_CONTESTED, UMUTEX_UNOWNED);
  
          umtxq_lock(&key);
          if (count != 0 && (owner & ~UMUTEX_CONTESTED) == 0)
                  umtxq_signal(&key, 1);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          return (0);
  }
  
  /*
   * Check if the mutex has waiters and tries to fix contention bit.
   */
  static int
  do_wake2_umutex(struct thread *td, struct umutex *m, uint32_t flags)
  {
          struct umtx_key key;
          uint32_t owner, old;
          int type;
          int error;
          int count;
  
          switch(flags & (UMUTEX_PRIO_INHERIT | UMUTEX_PRIO_PROTECT)) {
          case 0:
                  type = TYPE_NORMAL_UMUTEX;
                  break;
          case UMUTEX_PRIO_INHERIT:
                  type = TYPE_PI_UMUTEX;
                  break;
          case UMUTEX_PRIO_PROTECT:
                  type = TYPE_PP_UMUTEX;
                  break;
          default:
                  return (EINVAL);
          }
          if ((error = umtx_key_get(m, type, GET_SHARE(flags),
              &key)) != 0)
                  return (error);
  
          owner = 0;
          umtxq_lock(&key);
          umtxq_busy(&key);
          count = umtxq_count(&key);
          umtxq_unlock(&key);
          /*
           * Only repair contention bit if there is a waiter, this means the mutex
           * is still being referenced by userland code, otherwise don't update
           * any memory.
           */
          if (count > 1) {
                  owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
                  while ((owner & UMUTEX_CONTESTED) ==0) {
                          old = casuword32(&m->m_owner, owner,
                              owner|UMUTEX_CONTESTED);
                          if (old == owner)
                                  break;
                          owner = old;
                  }
          } else if (count == 1) {
                  owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
                  while ((owner & ~UMUTEX_CONTESTED) != 0 &&
                         (owner & UMUTEX_CONTESTED) == 0) {
                          old = casuword32(&m->m_owner, owner,
                              owner|UMUTEX_CONTESTED);
                          if (old == owner)
                                  break;
                          owner = old;
                  }
          }
          umtxq_lock(&key);
          if (owner == -1) {
                  error = EFAULT;
                  umtxq_signal(&key, INT_MAX);
          }
          else if (count != 0 && (owner & ~UMUTEX_CONTESTED) == 0)
                  umtxq_signal(&key, 1);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          return (error);
  }
  
  static inline struct umtx_pi *
  umtx_pi_alloc(int flags)
  {
          struct umtx_pi *pi;
  
          pi = uma_zalloc(umtx_pi_zone, M_ZERO | flags);
          TAILQ_INIT(&pi->pi_blocked);
          atomic_add_int(&umtx_pi_allocated, 1);
          return (pi);
  }
  
  static inline void
  umtx_pi_free(struct umtx_pi *pi)
  {
          uma_zfree(umtx_pi_zone, pi);
          atomic_add_int(&umtx_pi_allocated, -1);
  }
  
  /*
   * Adjust the thread's position on a pi_state after its priority has been
   * changed.
   */
  static int
  umtx_pi_adjust_thread(struct umtx_pi *pi, struct thread *td)
  {
          struct umtx_q *uq, *uq1, *uq2;
          struct thread *td1;
  
          mtx_assert(&umtx_lock, MA_OWNED);
          if (pi == NULL)
                  return (0);
  
          uq = td->td_umtxq;
  
          /*
           * Check if the thread needs to be moved on the blocked chain.
           * It needs to be moved if either its priority is lower than
           * the previous thread or higher than the next thread.
           */
          uq1 = TAILQ_PREV(uq, umtxq_head, uq_lockq);
          uq2 = TAILQ_NEXT(uq, uq_lockq);
          if ((uq1 != NULL && UPRI(td) < UPRI(uq1->uq_thread)) ||
              (uq2 != NULL && UPRI(td) > UPRI(uq2->uq_thread))) {
                  /*
                   * Remove thread from blocked chain and determine where
                   * it should be moved to.
                   */
                  TAILQ_REMOVE(&pi->pi_blocked, uq, uq_lockq);
                  TAILQ_FOREACH(uq1, &pi->pi_blocked, uq_lockq) {
                          td1 = uq1->uq_thread;
                          MPASS(td1->td_proc->p_magic == P_MAGIC);
                          if (UPRI(td1) > UPRI(td))
                                  break;
                  }
  
                  if (uq1 == NULL)
                          TAILQ_INSERT_TAIL(&pi->pi_blocked, uq, uq_lockq);
                  else
                          TAILQ_INSERT_BEFORE(uq1, uq, uq_lockq);
          }
          return (1);
  }
  
  /*
   * Propagate priority when a thread is blocked on POSIX
   * PI mutex.
   */ 
  static void
  umtx_propagate_priority(struct thread *td)
  {
          struct umtx_q *uq;
          struct umtx_pi *pi;
          int pri;
  
          mtx_assert(&umtx_lock, MA_OWNED);
          pri = UPRI(td);
          uq = td->td_umtxq;
          pi = uq->uq_pi_blocked;
          if (pi == NULL)
                  return;
  
          for (;;) {
                  td = pi->pi_owner;
                  if (td == NULL || td == curthread)
                          return;
  
                  MPASS(td->td_proc != NULL);
                  MPASS(td->td_proc->p_magic == P_MAGIC);
  
                  thread_lock(td);
                  if (td->td_lend_user_pri > pri)
                          sched_lend_user_prio(td, pri);
                  else {
                          thread_unlock(td);
                          break;
                  }
                  thread_unlock(td);
  
                  /*
                   * Pick up the lock that td is blocked on.
                   */
                  uq = td->td_umtxq;
                  pi = uq->uq_pi_blocked;
                  if (pi == NULL)
                          break;
                  /* Resort td on the list if needed. */
                  umtx_pi_adjust_thread(pi, td);
          }
  }
  
  /*
   * Unpropagate priority for a PI mutex when a thread blocked on
   * it is interrupted by signal or resumed by others.
   */
  static void
  umtx_repropagate_priority(struct umtx_pi *pi)
  {
          struct umtx_q *uq, *uq_owner;
          struct umtx_pi *pi2;
          int pri;
  
          mtx_assert(&umtx_lock, MA_OWNED);
  
          while (pi != NULL && pi->pi_owner != NULL) {
                  pri = PRI_MAX;
                  uq_owner = pi->pi_owner->td_umtxq;
  
                  TAILQ_FOREACH(pi2, &uq_owner->uq_pi_contested, pi_link) {
                          uq = TAILQ_FIRST(&pi2->pi_blocked);
                          if (uq != NULL) {
                                  if (pri > UPRI(uq->uq_thread))
                                          pri = UPRI(uq->uq_thread);
                          }
                  }
  
                  if (pri > uq_owner->uq_inherited_pri)
                          pri = uq_owner->uq_inherited_pri;
                  thread_lock(pi->pi_owner);
                  sched_lend_user_prio(pi->pi_owner, pri);
                  thread_unlock(pi->pi_owner);
                  if ((pi = uq_owner->uq_pi_blocked) != NULL)
                          umtx_pi_adjust_thread(pi, uq_owner->uq_thread);
          }
  }
  
  /*
   * Insert a PI mutex into owned list.
   */
  static void
  umtx_pi_setowner(struct umtx_pi *pi, struct thread *owner)
  {
          struct umtx_q *uq_owner;
  
          uq_owner = owner->td_umtxq;
          mtx_assert(&umtx_lock, MA_OWNED);
          if (pi->pi_owner != NULL)
                  panic("pi_ower != NULL");
          pi->pi_owner = owner;
          TAILQ_INSERT_TAIL(&uq_owner->uq_pi_contested, pi, pi_link);
  }
  
  /*
   * Claim ownership of a PI mutex.
   */
  static int
  umtx_pi_claim(struct umtx_pi *pi, struct thread *owner)
  {
          struct umtx_q *uq, *uq_owner;
  
          uq_owner = owner->td_umtxq;
          mtx_lock_spin(&umtx_lock);
          if (pi->pi_owner == owner) {
                  mtx_unlock_spin(&umtx_lock);
                  return (0);
          }
  
          if (pi->pi_owner != NULL) {
                  /*
                   * userland may have already messed the mutex, sigh.
                   */
                  mtx_unlock_spin(&umtx_lock);
                  return (EPERM);
          }
          umtx_pi_setowner(pi, owner);
          uq = TAILQ_FIRST(&pi->pi_blocked);
          if (uq != NULL) {
                  int pri;
  
                  pri = UPRI(uq->uq_thread);
                  thread_lock(owner);
                  if (pri < UPRI(owner))
                          sched_lend_user_prio(owner, pri);
                  thread_unlock(owner);
          }
          mtx_unlock_spin(&umtx_lock);
          return (0);
  }
  
  /*
   * Adjust a thread's order position in its blocked PI mutex,
   * this may result new priority propagating process.
   */
  void
  umtx_pi_adjust(struct thread *td, u_char oldpri)
  {
          struct umtx_q *uq;
          struct umtx_pi *pi;
  
          uq = td->td_umtxq;
          mtx_lock_spin(&umtx_lock);
          /*
           * Pick up the lock that td is blocked on.
           */
          pi = uq->uq_pi_blocked;
          if (pi != NULL) {
                  umtx_pi_adjust_thread(pi, td);
                  umtx_repropagate_priority(pi);
          }
          mtx_unlock_spin(&umtx_lock);
  }
  
  /*
   * Sleep on a PI mutex.
   */
  static int
  umtxq_sleep_pi(struct umtx_q *uq, struct umtx_pi *pi,
          uint32_t owner, const char *wmesg, int timo)
  {
          struct umtxq_chain *uc;
          struct thread *td, *td1;
          struct umtx_q *uq1;
          int pri;
          int error = 0;
  
          td = uq->uq_thread;
          KASSERT(td == curthread, ("inconsistent uq_thread"));
          uc = umtxq_getchain(&uq->uq_key);
          UMTXQ_LOCKED_ASSERT(uc);
          UMTXQ_BUSY_ASSERT(uc);
          umtxq_insert(uq);
          mtx_lock_spin(&umtx_lock);
          if (pi->pi_owner == NULL) {
                  mtx_unlock_spin(&umtx_lock);
                  /* XXX Only look up thread in current process. */
                  td1 = tdfind(owner, curproc->p_pid);
                  mtx_lock_spin(&umtx_lock);
                  if (td1 != NULL) {
                          if (pi->pi_owner == NULL)
                                  umtx_pi_setowner(pi, td1);
                          PROC_UNLOCK(td1->td_proc);
                  }
          }
  
          TAILQ_FOREACH(uq1, &pi->pi_blocked, uq_lockq) {
                  pri = UPRI(uq1->uq_thread);
                  if (pri > UPRI(td))
                          break;
          }
  
          if (uq1 != NULL)
                  TAILQ_INSERT_BEFORE(uq1, uq, uq_lockq);
          else
                  TAILQ_INSERT_TAIL(&pi->pi_blocked, uq, uq_lockq);
  
          uq->uq_pi_blocked = pi;
          thread_lock(td);
          td->td_flags |= TDF_UPIBLOCKED;
          thread_unlock(td);
          umtx_propagate_priority(td);
          mtx_unlock_spin(&umtx_lock);
          umtxq_unbusy(&uq->uq_key);
  
          if (uq->uq_flags & UQF_UMTXQ) {
                  error = msleep(uq, &uc->uc_lock, PCATCH, wmesg, timo);
                  if (error == EWOULDBLOCK)
                          error = ETIMEDOUT;
                  if (uq->uq_flags & UQF_UMTXQ) {
                          umtxq_remove(uq);
                  }
          }
          mtx_lock_spin(&umtx_lock);
          uq->uq_pi_blocked = NULL;
          thread_lock(td);
          td->td_flags &= ~TDF_UPIBLOCKED;
          thread_unlock(td);
          TAILQ_REMOVE(&pi->pi_blocked, uq, uq_lockq);
          umtx_repropagate_priority(pi);
          mtx_unlock_spin(&umtx_lock);
          umtxq_unlock(&uq->uq_key);
  
          return (error);
  }
  
  /*
   * Add reference count for a PI mutex.
   */
  static void
  umtx_pi_ref(struct umtx_pi *pi)
  {
          struct umtxq_chain *uc;
  
          uc = umtxq_getchain(&pi->pi_key);
          UMTXQ_LOCKED_ASSERT(uc);
          pi->pi_refcount++;
  }
  
  /*
   * Decrease reference count for a PI mutex, if the counter
   * is decreased to zero, its memory space is freed.
   */ 
  static void
  umtx_pi_unref(struct umtx_pi *pi)
  {
          struct umtxq_chain *uc;
  
          uc = umtxq_getchain(&pi->pi_key);
          UMTXQ_LOCKED_ASSERT(uc);
          KASSERT(pi->pi_refcount > 0, ("invalid reference count"));
          if (--pi->pi_refcount == 0) {
                  mtx_lock_spin(&umtx_lock);
                  if (pi->pi_owner != NULL) {
                          TAILQ_REMOVE(&pi->pi_owner->td_umtxq->uq_pi_contested,
                                  pi, pi_link);
                          pi->pi_owner = NULL;
                  }
                  KASSERT(TAILQ_EMPTY(&pi->pi_blocked),
                          ("blocked queue not empty"));
                  mtx_unlock_spin(&umtx_lock);
                  TAILQ_REMOVE(&uc->uc_pi_list, pi, pi_hashlink);
                  umtx_pi_free(pi);
          }
  }
  
  /*
   * Find a PI mutex in hash table.
   */
  static struct umtx_pi *
  umtx_pi_lookup(struct umtx_key *key)
  {
          struct umtxq_chain *uc;
          struct umtx_pi *pi;
  
          uc = umtxq_getchain(key);
          UMTXQ_LOCKED_ASSERT(uc);
  
          TAILQ_FOREACH(pi, &uc->uc_pi_list, pi_hashlink) {
                  if (umtx_key_match(&pi->pi_key, key)) {
                          return (pi);
                  }
          }
          return (NULL);
  }
  
  /*
   * Insert a PI mutex into hash table.
   */
  static inline void
  umtx_pi_insert(struct umtx_pi *pi)
  {
          struct umtxq_chain *uc;
  
          uc = umtxq_getchain(&pi->pi_key);
          UMTXQ_LOCKED_ASSERT(uc);
          TAILQ_INSERT_TAIL(&uc->uc_pi_list, pi, pi_hashlink);
  }
  
  /*
   * Lock a PI mutex.
   */
  static int
  _do_lock_pi(struct thread *td, struct umutex *m, uint32_t flags, int timo,
          int try)
  {
          struct umtx_q *uq;
          struct umtx_pi *pi, *new_pi;
          uint32_t id, owner, old;
          int error;
  
          id = td->td_tid;
          uq = td->td_umtxq;
  
          if ((error = umtx_key_get(m, TYPE_PI_UMUTEX, GET_SHARE(flags),
              &uq->uq_key)) != 0)
                  return (error);
          umtxq_lock(&uq->uq_key);
          pi = umtx_pi_lookup(&uq->uq_key);
          if (pi == NULL) {
                  new_pi = umtx_pi_alloc(M_NOWAIT);
                  if (new_pi == NULL) {
                          umtxq_unlock(&uq->uq_key);
                          new_pi = umtx_pi_alloc(M_WAITOK);
                          umtxq_lock(&uq->uq_key);
                          pi = umtx_pi_lookup(&uq->uq_key);
                          if (pi != NULL) {
                                  umtx_pi_free(new_pi);
                                  new_pi = NULL;
                          }
                  }
                  if (new_pi != NULL) {
                          new_pi->pi_key = uq->uq_key;
                          umtx_pi_insert(new_pi);
                          pi = new_pi;
                  }
          }
          umtx_pi_ref(pi);
          umtxq_unlock(&uq->uq_key);
  
          /*
           * Care must be exercised when dealing with umtx structure.  It
           * can fault on any access.
           */
          for (;;) {
                  /*
                   * Try the uncontested case.  This should be done in userland.
                   */
                  owner = casuword32(&m->m_owner, UMUTEX_UNOWNED, id);
  
                  /* The acquire succeeded. */
                  if (owner == UMUTEX_UNOWNED) {
                          error = 0;
                          break;
                  }
  
                  /* The address was invalid. */
                  if (owner == -1) {
                          error = EFAULT;
                          break;
                  }
  
                  /* If no one owns it but it is contested try to acquire it. */
                  if (owner == UMUTEX_CONTESTED) {
                          owner = casuword32(&m->m_owner,
                              UMUTEX_CONTESTED, id | UMUTEX_CONTESTED);
  
                          if (owner == UMUTEX_CONTESTED) {
                                  umtxq_lock(&uq->uq_key);
                                  umtxq_busy(&uq->uq_key);
                                  error = umtx_pi_claim(pi, td);
                                  umtxq_unbusy(&uq->uq_key);
                                  umtxq_unlock(&uq->uq_key);
                                  break;
                          }
  
                          /* The address was invalid. */
                          if (owner == -1) {
                                  error = EFAULT;
                                  break;
                          }
  
                          /* If this failed the lock has changed, restart. */
                          continue;
                  }
  
                  if ((flags & UMUTEX_ERROR_CHECK) != 0 &&
                      (owner & ~UMUTEX_CONTESTED) == id) {
                          error = EDEADLK;
                          break;
                  }
  
                  if (try != 0) {
                          error = EBUSY;
                          break;
                  }
  
                  /*
                   * If we caught a signal, we have retried and now
                   * exit immediately.
                   */
                  if (error != 0)
                          break;
                          
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
  
                  /*
                   * Set the contested bit so that a release in user space
                   * knows to use the system call for unlock.  If this fails
                   * either some one else has acquired the lock or it has been
                   * released.
                   */
                  old = casuword32(&m->m_owner, owner, owner | UMUTEX_CONTESTED);
  
                  /* The address was invalid. */
                  if (old == -1) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_unbusy(&uq->uq_key);
                          umtxq_unlock(&uq->uq_key);
                          error = EFAULT;
                          break;
                  }
  
                  umtxq_lock(&uq->uq_key);
                  /*
                   * We set the contested bit, sleep. Otherwise the lock changed
                   * and we need to retry or we lost a race to the thread
                   * unlocking the umtx.
                   */
                  if (old == owner)
                          error = umtxq_sleep_pi(uq, pi, owner & ~UMUTEX_CONTESTED,
                                   "umtxpi", timo);
                  else {
                          umtxq_unbusy(&uq->uq_key);
                          umtxq_unlock(&uq->uq_key);
                  }
          }
  
          umtxq_lock(&uq->uq_key);
          umtx_pi_unref(pi);
          umtxq_unlock(&uq->uq_key);
  
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  /*
   * Unlock a PI mutex.
   */
  static int
  do_unlock_pi(struct thread *td, struct umutex *m, uint32_t flags)
  {
          struct umtx_key key;
          struct umtx_q *uq_first, *uq_first2, *uq_me;
          struct umtx_pi *pi, *pi2;
          uint32_t owner, old, id;
          int error;
          int count;
          int pri;
  
          id = td->td_tid;
          /*
           * Make sure we own this mtx.
           */
          owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
          if (owner == -1)
                  return (EFAULT);
  
          if ((owner & ~UMUTEX_CONTESTED) != id)
                  return (EPERM);
  
          /* This should be done in userland */
          if ((owner & UMUTEX_CONTESTED) == 0) {
                  old = casuword32(&m->m_owner, owner, UMUTEX_UNOWNED);
                  if (old == -1)
                          return (EFAULT);
                  if (old == owner)
                          return (0);
                  owner = old;
          }
  
          /* We should only ever be in here for contested locks */
          if ((error = umtx_key_get(m, TYPE_PI_UMUTEX, GET_SHARE(flags),
              &key)) != 0)
                  return (error);
  
          umtxq_lock(&key);
          umtxq_busy(&key);
          count = umtxq_count_pi(&key, &uq_first);
          if (uq_first != NULL) {
                  mtx_lock_spin(&umtx_lock);
                  pi = uq_first->uq_pi_blocked;
                  KASSERT(pi != NULL, ("pi == NULL?"));
                  if (pi->pi_owner != curthread) {
                          mtx_unlock_spin(&umtx_lock);
                          umtxq_unbusy(&key);
                          umtxq_unlock(&key);
                          umtx_key_release(&key);
                          /* userland messed the mutex */
                          return (EPERM);
                  }
                  uq_me = curthread->td_umtxq;
                  pi->pi_owner = NULL;
                  TAILQ_REMOVE(&uq_me->uq_pi_contested, pi, pi_link);
                  /* get highest priority thread which is still sleeping. */
                  uq_first = TAILQ_FIRST(&pi->pi_blocked);
                  while (uq_first != NULL && 
                         (uq_first->uq_flags & UQF_UMTXQ) == 0) {
                          uq_first = TAILQ_NEXT(uq_first, uq_lockq);
                  }
                  pri = PRI_MAX;
                  TAILQ_FOREACH(pi2, &uq_me->uq_pi_contested, pi_link) {
                          uq_first2 = TAILQ_FIRST(&pi2->pi_blocked);
                          if (uq_first2 != NULL) {
                                  if (pri > UPRI(uq_first2->uq_thread))
                                          pri = UPRI(uq_first2->uq_thread);
                          }
                  }
                  thread_lock(curthread);
                  sched_lend_user_prio(curthread, pri);
                  thread_unlock(curthread);
                  mtx_unlock_spin(&umtx_lock);
                  if (uq_first)
                          umtxq_signal_thread(uq_first);
          }
          umtxq_unlock(&key);
  
          /*
           * When unlocking the umtx, it must be marked as unowned if
           * there is zero or one thread only waiting for it.
           * Otherwise, it must be marked as contested.
           */
          old = casuword32(&m->m_owner, owner,
                  count <= 1 ? UMUTEX_UNOWNED : UMUTEX_CONTESTED);
  
          umtxq_lock(&key);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          if (old == -1)
                  return (EFAULT);
          if (old != owner)
                  return (EINVAL);
          return (0);
  }
  
  /*
   * Lock a PP mutex.
   */
  static int
  _do_lock_pp(struct thread *td, struct umutex *m, uint32_t flags, int timo,
          int try)
  {
          struct umtx_q *uq, *uq2;
          struct umtx_pi *pi;
          uint32_t ceiling;
          uint32_t owner, id;
          int error, pri, old_inherited_pri, su;
  
          id = td->td_tid;
          uq = td->td_umtxq;
          if ((error = umtx_key_get(m, TYPE_PP_UMUTEX, GET_SHARE(flags),
              &uq->uq_key)) != 0)
                  return (error);
          su = (priv_check(td, PRIV_SCHED_RTPRIO) == 0);
          for (;;) {
                  old_inherited_pri = uq->uq_inherited_pri;
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
  
                  ceiling = RTP_PRIO_MAX - fuword32(&m->m_ceilings[0]);
                  if (ceiling > RTP_PRIO_MAX) {
                          error = EINVAL;
                          goto out;
                  }
  
                  mtx_lock_spin(&umtx_lock);
                  if (UPRI(td) < PRI_MIN_REALTIME + ceiling) {
                          mtx_unlock_spin(&umtx_lock);
                          error = EINVAL;
                          goto out;
                  }
                  if (su && PRI_MIN_REALTIME + ceiling < uq->uq_inherited_pri) {
                          uq->uq_inherited_pri = PRI_MIN_REALTIME + ceiling;
                          thread_lock(td);
                          if (uq->uq_inherited_pri < UPRI(td))
                                  sched_lend_user_prio(td, uq->uq_inherited_pri);
                          thread_unlock(td);
                  }
                  mtx_unlock_spin(&umtx_lock);
  
                  owner = casuword32(&m->m_owner,
                      UMUTEX_CONTESTED, id | UMUTEX_CONTESTED);
  
                  if (owner == UMUTEX_CONTESTED) {
                          error = 0;
                          break;
                  }
  
                  /* The address was invalid. */
                  if (owner == -1) {
                          error = EFAULT;
                          break;
                  }
  
                  if ((flags & UMUTEX_ERROR_CHECK) != 0 &&
                      (owner & ~UMUTEX_CONTESTED) == id) {
                          error = EDEADLK;
                          break;
                  }
  
                  if (try != 0) {
                          error = EBUSY;
                          break;
                  }
  
                  /*
                   * If we caught a signal, we have retried and now
                   * exit immediately.
                   */
                  if (error != 0)
                          break;
  
                  umtxq_lock(&uq->uq_key);
                  umtxq_insert(uq);
                  umtxq_unbusy(&uq->uq_key);
                  error = umtxq_sleep(uq, "umtxpp", timo);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
  
                  mtx_lock_spin(&umtx_lock);
                  uq->uq_inherited_pri = old_inherited_pri;
                  pri = PRI_MAX;
                  TAILQ_FOREACH(pi, &uq->uq_pi_contested, pi_link) {
                          uq2 = TAILQ_FIRST(&pi->pi_blocked);
                          if (uq2 != NULL) {
                                  if (pri > UPRI(uq2->uq_thread))
                                          pri = UPRI(uq2->uq_thread);
                          }
                  }
                  if (pri > uq->uq_inherited_pri)
                          pri = uq->uq_inherited_pri;
                  thread_lock(td);
                  sched_lend_user_prio(td, pri);
                  thread_unlock(td);
                  mtx_unlock_spin(&umtx_lock);
          }
  
          if (error != 0) {
                  mtx_lock_spin(&umtx_lock);
                  uq->uq_inherited_pri = old_inherited_pri;
                  pri = PRI_MAX;
                  TAILQ_FOREACH(pi, &uq->uq_pi_contested, pi_link) {
                          uq2 = TAILQ_FIRST(&pi->pi_blocked);
                          if (uq2 != NULL) {
                                  if (pri > UPRI(uq2->uq_thread))
                                          pri = UPRI(uq2->uq_thread);
                          }
                  }
                  if (pri > uq->uq_inherited_pri)
                          pri = uq->uq_inherited_pri;
                  thread_lock(td);
                  sched_lend_user_prio(td, pri);
                  thread_unlock(td);
                  mtx_unlock_spin(&umtx_lock);
          }
  
  out:
          umtxq_lock(&uq->uq_key);
          umtxq_unbusy(&uq->uq_key);
          umtxq_unlock(&uq->uq_key);
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  /*
   * Unlock a PP mutex.
   */
  static int
  do_unlock_pp(struct thread *td, struct umutex *m, uint32_t flags)
  {
          struct umtx_key key;
          struct umtx_q *uq, *uq2;
          struct umtx_pi *pi;
          uint32_t owner, id;
          uint32_t rceiling;
          int error, pri, new_inherited_pri, su;
  
          id = td->td_tid;
          uq = td->td_umtxq;
          su = (priv_check(td, PRIV_SCHED_RTPRIO) == 0);
  
          /*
           * Make sure we own this mtx.
           */
          owner = fuword32(__DEVOLATILE(uint32_t *, &m->m_owner));
          if (owner == -1)
                  return (EFAULT);
  
          if ((owner & ~UMUTEX_CONTESTED) != id)
                  return (EPERM);
  
          error = copyin(&m->m_ceilings[1], &rceiling, sizeof(uint32_t));
          if (error != 0)
                  return (error);
  
          if (rceiling == -1)
                  new_inherited_pri = PRI_MAX;
          else {
                  rceiling = RTP_PRIO_MAX - rceiling;
                  if (rceiling > RTP_PRIO_MAX)
                          return (EINVAL);
                  new_inherited_pri = PRI_MIN_REALTIME + rceiling;
          }
  
          if ((error = umtx_key_get(m, TYPE_PP_UMUTEX, GET_SHARE(flags),
              &key)) != 0)
                  return (error);
          umtxq_lock(&key);
          umtxq_busy(&key);
          umtxq_unlock(&key);
          /*
           * For priority protected mutex, always set unlocked state
           * to UMUTEX_CONTESTED, so that userland always enters kernel
           * to lock the mutex, it is necessary because thread priority
           * has to be adjusted for such mutex.
           */
          error = suword32(__DEVOLATILE(uint32_t *, &m->m_owner),
                  UMUTEX_CONTESTED);
  
          umtxq_lock(&key);
          if (error == 0)
                  umtxq_signal(&key, 1);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
  
          if (error == -1)
                  error = EFAULT;
          else {
                  mtx_lock_spin(&umtx_lock);
                  if (su != 0)
                          uq->uq_inherited_pri = new_inherited_pri;
                  pri = PRI_MAX;
                  TAILQ_FOREACH(pi, &uq->uq_pi_contested, pi_link) {
                          uq2 = TAILQ_FIRST(&pi->pi_blocked);
                          if (uq2 != NULL) {
                                  if (pri > UPRI(uq2->uq_thread))
                                          pri = UPRI(uq2->uq_thread);
                          }
                  }
                  if (pri > uq->uq_inherited_pri)
                          pri = uq->uq_inherited_pri;
                  thread_lock(td);
                  sched_lend_user_prio(td, pri);
                  thread_unlock(td);
                  mtx_unlock_spin(&umtx_lock);
          }
          umtx_key_release(&key);
          return (error);
  }
  
  static int
  do_set_ceiling(struct thread *td, struct umutex *m, uint32_t ceiling,
          uint32_t *old_ceiling)
  {
          struct umtx_q *uq;
          uint32_t save_ceiling;
          uint32_t owner, id;
          uint32_t flags;
          int error;
  
          flags = fuword32(&m->m_flags);
          if ((flags & UMUTEX_PRIO_PROTECT) == 0)
                  return (EINVAL);
          if (ceiling > RTP_PRIO_MAX)
                  return (EINVAL);
          id = td->td_tid;
          uq = td->td_umtxq;
          if ((error = umtx_key_get(m, TYPE_PP_UMUTEX, GET_SHARE(flags),
             &uq->uq_key)) != 0)
                  return (error);
          for (;;) {
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
  
                  save_ceiling = fuword32(&m->m_ceilings[0]);
  
                  owner = casuword32(&m->m_owner,
                      UMUTEX_CONTESTED, id | UMUTEX_CONTESTED);
  
                  if (owner == UMUTEX_CONTESTED) {
                          suword32(&m->m_ceilings[0], ceiling);
                          suword32(__DEVOLATILE(uint32_t *, &m->m_owner),
                                  UMUTEX_CONTESTED);
                          error = 0;
                          break;
                  }
  
                  /* The address was invalid. */
                  if (owner == -1) {
                          error = EFAULT;
                          break;
                  }
  
                  if ((owner & ~UMUTEX_CONTESTED) == id) {
                          suword32(&m->m_ceilings[0], ceiling);
                          error = 0;
                          break;
                  }
  
                  /*
                   * If we caught a signal, we have retried and now
                   * exit immediately.
                   */
                  if (error != 0)
                          break;
  
                  /*
                   * We set the contested bit, sleep. Otherwise the lock changed
                   * and we need to retry or we lost a race to the thread
                   * unlocking the umtx.
                   */
                  umtxq_lock(&uq->uq_key);
                  umtxq_insert(uq);
                  umtxq_unbusy(&uq->uq_key);
                  error = umtxq_sleep(uq, "umtxpp", 0);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
          }
          umtxq_lock(&uq->uq_key);
          if (error == 0)
                  umtxq_signal(&uq->uq_key, INT_MAX);
          umtxq_unbusy(&uq->uq_key);
          umtxq_unlock(&uq->uq_key);
          umtx_key_release(&uq->uq_key);
          if (error == 0 && old_ceiling != NULL)
                  suword32(old_ceiling, save_ceiling);
          return (error);
  }
  
  static int
  _do_lock_umutex(struct thread *td, struct umutex *m, int flags, int timo,
          int mode)
  {
          switch(flags & (UMUTEX_PRIO_INHERIT | UMUTEX_PRIO_PROTECT)) {
          case 0:
                  return (_do_lock_normal(td, m, flags, timo, mode));
          case UMUTEX_PRIO_INHERIT:
                  return (_do_lock_pi(td, m, flags, timo, mode));
          case UMUTEX_PRIO_PROTECT:
                  return (_do_lock_pp(td, m, flags, timo, mode));
          }
          return (EINVAL);
  }
  
  /*
   * Lock a userland POSIX mutex.
   */
  static int
  do_lock_umutex(struct thread *td, struct umutex *m,
          struct timespec *timeout, int mode)
  {
          struct timespec ts, ts2, ts3;
          struct timeval tv;
          uint32_t flags;
          int error;
  
          flags = fuword32(&m->m_flags);
          if (flags == -1)
                  return (EFAULT);
  
          if (timeout == NULL) {
                  error = _do_lock_umutex(td, m, flags, 0, mode);
                  /* Mutex locking is restarted if it is interrupted. */
                  if (error == EINTR && mode != _UMUTEX_WAIT)
                          error = ERESTART;
          } else {
                  getnanouptime(&ts);
                  timespecadd(&ts, timeout);
                  TIMESPEC_TO_TIMEVAL(&tv, timeout);
                  for (;;) {
                          error = _do_lock_umutex(td, m, flags, tvtohz(&tv), mode);
                          if (error != ETIMEDOUT)
                                  break;
                          getnanouptime(&ts2);
                          if (timespeccmp(&ts2, &ts, >=)) {
                                  error = ETIMEDOUT;
                                  break;
                          }
                          ts3 = ts;
                          timespecsub(&ts3, &ts2);
                          TIMESPEC_TO_TIMEVAL(&tv, &ts3);
                  }
                  /* Timed-locking is not restarted. */
                  if (error == ERESTART)
                          error = EINTR;
          }
          return (error);
  }
  
  /*
   * Unlock a userland POSIX mutex.
   */
  static int
  do_unlock_umutex(struct thread *td, struct umutex *m)
  {
          uint32_t flags;
  
          flags = fuword32(&m->m_flags);
          if (flags == -1)
                  return (EFAULT);
  
          switch(flags & (UMUTEX_PRIO_INHERIT | UMUTEX_PRIO_PROTECT)) {
          case 0:
                  return (do_unlock_normal(td, m, flags));
          case UMUTEX_PRIO_INHERIT:
                  return (do_unlock_pi(td, m, flags));
          case UMUTEX_PRIO_PROTECT:
                  return (do_unlock_pp(td, m, flags));
          }
  
          return (EINVAL);
  }
  
  static int
  do_cv_wait(struct thread *td, struct ucond *cv, struct umutex *m,
          struct timespec *timeout, u_long wflags)
  {
          struct umtx_q *uq;
          struct timeval tv;
          struct timespec cts, ets, tts;
          uint32_t flags;
          uint32_t clockid;
          int error;
  
          uq = td->td_umtxq;
          flags = fuword32(&cv->c_flags);
          error = umtx_key_get(cv, TYPE_CV, GET_SHARE(flags), &uq->uq_key);
          if (error != 0)
                  return (error);
  
          if ((wflags & CVWAIT_CLOCKID) != 0) {
                  clockid = fuword32(&cv->c_clockid);
                  if (clockid < CLOCK_REALTIME ||
                      clockid >= CLOCK_THREAD_CPUTIME_ID) {
                          /* hmm, only HW clock id will work. */
                          return (EINVAL);
                  }
          } else {
                  clockid = CLOCK_REALTIME;
          }
  
          umtxq_lock(&uq->uq_key);
          umtxq_busy(&uq->uq_key);
          umtxq_insert(uq);
          umtxq_unlock(&uq->uq_key);
  
          /*
           * Set c_has_waiters to 1 before releasing user mutex, also
           * don't modify cache line when unnecessary.
           */
          if (fuword32(__DEVOLATILE(uint32_t *, &cv->c_has_waiters)) == 0)
                  suword32(__DEVOLATILE(uint32_t *, &cv->c_has_waiters), 1);
  
          umtxq_lock(&uq->uq_key);
          umtxq_unbusy(&uq->uq_key);
          umtxq_unlock(&uq->uq_key);
  
          error = do_unlock_umutex(td, m);
          
          umtxq_lock(&uq->uq_key);
          if (error == 0) {
                  if (timeout == NULL) {
                          error = umtxq_sleep(uq, "ucond", 0);
                  } else {
                          if ((wflags & CVWAIT_ABSTIME) == 0) {
                                  kern_clock_gettime(td, clockid, &ets);
                                  timespecadd(&ets, timeout);
                                  tts = *timeout;
                          } else { /* absolute time */
                                  ets = *timeout;
                                  tts = *timeout;
                                  kern_clock_gettime(td, clockid, &cts);
                                  timespecsub(&tts, &cts);
                          }
                          TIMESPEC_TO_TIMEVAL(&tv, &tts);
                          for (;;) {
                                  error = umtxq_sleep(uq, "ucond", tvtohz(&tv));
                                  if (error != ETIMEDOUT)
                                          break;
                                  kern_clock_gettime(td, clockid, &cts);
                                  if (timespeccmp(&cts, &ets, >=)) {
                                          error = ETIMEDOUT;
                                          break;
                                  }
                                  tts = ets;
                                  timespecsub(&tts, &cts);
                                  TIMESPEC_TO_TIMEVAL(&tv, &tts);
                          }
                  }
          }
  
          if ((uq->uq_flags & UQF_UMTXQ) == 0)
                  error = 0;
          else {
                  /*
                   * This must be timeout,interrupted by signal or
                   * surprious wakeup, clear c_has_waiter flag when
                   * necessary.
                   */
                  umtxq_busy(&uq->uq_key);
                  if ((uq->uq_flags & UQF_UMTXQ) != 0) {
                          int oldlen = uq->uq_cur_queue->length;
                          umtxq_remove(uq);
                          if (oldlen == 1) {
                                  umtxq_unlock(&uq->uq_key);
                                  suword32(
                                      __DEVOLATILE(uint32_t *,
                                           &cv->c_has_waiters), 0);
                                  umtxq_lock(&uq->uq_key);
                          }
                  }
                  umtxq_unbusy(&uq->uq_key);
                  if (error == ERESTART)
                          error = EINTR;
          }
  
          umtxq_unlock(&uq->uq_key);
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  /*
   * Signal a userland condition variable.
   */
  static int
  do_cv_signal(struct thread *td, struct ucond *cv)
  {
          struct umtx_key key;
          int error, cnt, nwake;
          uint32_t flags;
  
          flags = fuword32(&cv->c_flags);
          if ((error = umtx_key_get(cv, TYPE_CV, GET_SHARE(flags), &key)) != 0)
                  return (error); 
          umtxq_lock(&key);
          umtxq_busy(&key);
          cnt = umtxq_count(&key);
          nwake = umtxq_signal(&key, 1);
          if (cnt <= nwake) {
                  umtxq_unlock(&key);
                  error = suword32(
                      __DEVOLATILE(uint32_t *, &cv->c_has_waiters), 0);
                  umtxq_lock(&key);
          }
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          return (error);
  }
  
  static int
  do_cv_broadcast(struct thread *td, struct ucond *cv)
  {
          struct umtx_key key;
          int error;
          uint32_t flags;
  
          flags = fuword32(&cv->c_flags);
          if ((error = umtx_key_get(cv, TYPE_CV, GET_SHARE(flags), &key)) != 0)
                  return (error); 
  
          umtxq_lock(&key);
          umtxq_busy(&key);
          umtxq_signal(&key, INT_MAX);
          umtxq_unlock(&key);
  
          error = suword32(__DEVOLATILE(uint32_t *, &cv->c_has_waiters), 0);
  
          umtxq_lock(&key);
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
  
          umtx_key_release(&key);
          return (error);
  }
  
  static int
  do_rw_rdlock(struct thread *td, struct urwlock *rwlock, long fflag, int timo)
  {
          struct umtx_q *uq;
          uint32_t flags, wrflags;
          int32_t state, oldstate;
          int32_t blocked_readers;
          int error;
  
          uq = td->td_umtxq;
          flags = fuword32(&rwlock->rw_flags);
          error = umtx_key_get(rwlock, TYPE_RWLOCK, GET_SHARE(flags), &uq->uq_key);
          if (error != 0)
                  return (error);
  
          wrflags = URWLOCK_WRITE_OWNER;
          if (!(fflag & URWLOCK_PREFER_READER) && !(flags & URWLOCK_PREFER_READER))
                  wrflags |= URWLOCK_WRITE_WAITERS;
  
          for (;;) {
                  state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                  /* try to lock it */
                  while (!(state & wrflags)) {
                          if (__predict_false(URWLOCK_READER_COUNT(state) == URWLOCK_MAX_READERS)) {
                                  umtx_key_release(&uq->uq_key);
                                  return (EAGAIN);
                          }
                          oldstate = casuword32(&rwlock->rw_state, state, state + 1);
                          if (oldstate == state) {
                                  umtx_key_release(&uq->uq_key);
                                  return (0);
                          }
                          state = oldstate;
                  }
  
                  if (error)
                          break;
  
                  /* grab monitor lock */
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
  
                  /*
                   * re-read the state, in case it changed between the try-lock above
                   * and the check below
                   */
                  state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
  
                  /* set read contention bit */
                  while ((state & wrflags) && !(state & URWLOCK_READ_WAITERS)) {
                          oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_READ_WAITERS);
                          if (oldstate == state)
                                  goto sleep;
                          state = oldstate;
                  }
  
                  /* state is changed while setting flags, restart */
                  if (!(state & wrflags)) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_unbusy(&uq->uq_key);
                          umtxq_unlock(&uq->uq_key);
                          continue;
                  }
  
  sleep:
                  /* contention bit is set, before sleeping, increase read waiter count */
                  blocked_readers = fuword32(&rwlock->rw_blocked_readers);
                  suword32(&rwlock->rw_blocked_readers, blocked_readers+1);
  
                  while (state & wrflags) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_insert(uq);
                          umtxq_unbusy(&uq->uq_key);
  
                          error = umtxq_sleep(uq, "urdlck", timo);
  
                          umtxq_busy(&uq->uq_key);
                          umtxq_remove(uq);
                          umtxq_unlock(&uq->uq_key);
                          if (error)
                                  break;
                          state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                  }
  
                  /* decrease read waiter count, and may clear read contention bit */
                  blocked_readers = fuword32(&rwlock->rw_blocked_readers);
                  suword32(&rwlock->rw_blocked_readers, blocked_readers-1);
                  if (blocked_readers == 1) {
                          state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                          for (;;) {
                                  oldstate = casuword32(&rwlock->rw_state, state,
                                           state & ~URWLOCK_READ_WAITERS);
                                  if (oldstate == state)
                                          break;
                                  state = oldstate;
                          }
                  }
  
                  umtxq_lock(&uq->uq_key);
                  umtxq_unbusy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
          }
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  static int
  do_rw_rdlock2(struct thread *td, void *obj, long val, struct timespec *timeout)
  {
          struct timespec ts, ts2, ts3;
          struct timeval tv;
          int error;
  
          getnanouptime(&ts);
          timespecadd(&ts, timeout);
          TIMESPEC_TO_TIMEVAL(&tv, timeout);
          for (;;) {
                  error = do_rw_rdlock(td, obj, val, tvtohz(&tv));
                  if (error != ETIMEDOUT)
                          break;
                  getnanouptime(&ts2);
                  if (timespeccmp(&ts2, &ts, >=)) {
                          error = ETIMEDOUT;
                          break;
                  }
                  ts3 = ts;
                  timespecsub(&ts3, &ts2);
                  TIMESPEC_TO_TIMEVAL(&tv, &ts3);
          }
          if (error == ERESTART)
                  error = EINTR;
          return (error);
  }
  
  static int
  do_rw_wrlock(struct thread *td, struct urwlock *rwlock, int timo)
  {
          struct umtx_q *uq;
          uint32_t flags;
          int32_t state, oldstate;
          int32_t blocked_writers;
          int32_t blocked_readers;
          int error;
  
          uq = td->td_umtxq;
          flags = fuword32(&rwlock->rw_flags);
          error = umtx_key_get(rwlock, TYPE_RWLOCK, GET_SHARE(flags), &uq->uq_key);
          if (error != 0)
                  return (error);
  
          blocked_readers = 0;
          for (;;) {
                  state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                  while (!(state & URWLOCK_WRITE_OWNER) && URWLOCK_READER_COUNT(state) == 0) {
                          oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_WRITE_OWNER);
                          if (oldstate == state) {
                                  umtx_key_release(&uq->uq_key);
                                  return (0);
                          }
                          state = oldstate;
                  }
  
                  if (error) {
                          if (!(state & (URWLOCK_WRITE_OWNER|URWLOCK_WRITE_WAITERS)) &&
                              blocked_readers != 0) {
                                  umtxq_lock(&uq->uq_key);
                                  umtxq_busy(&uq->uq_key);
                                  umtxq_signal_queue(&uq->uq_key, INT_MAX, UMTX_SHARED_QUEUE);
                                  umtxq_unbusy(&uq->uq_key);
                                  umtxq_unlock(&uq->uq_key);
                          }
  
                          break;
                  }
  
                  /* grab monitor lock */
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
  
                  /*
                   * re-read the state, in case it changed between the try-lock above
                   * and the check below
                   */
                  state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
  
                  while (((state & URWLOCK_WRITE_OWNER) || URWLOCK_READER_COUNT(state) != 0) &&
                         (state & URWLOCK_WRITE_WAITERS) == 0) {
                          oldstate = casuword32(&rwlock->rw_state, state, state | URWLOCK_WRITE_WAITERS);
                          if (oldstate == state)
                                  goto sleep;
                          state = oldstate;
                  }
  
                  if (!(state & URWLOCK_WRITE_OWNER) && URWLOCK_READER_COUNT(state) == 0) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_unbusy(&uq->uq_key);
                          umtxq_unlock(&uq->uq_key);
                          continue;
                  }
  sleep:
                  blocked_writers = fuword32(&rwlock->rw_blocked_writers);
                  suword32(&rwlock->rw_blocked_writers, blocked_writers+1);
  
                  while ((state & URWLOCK_WRITE_OWNER) || URWLOCK_READER_COUNT(state) != 0) {
                          umtxq_lock(&uq->uq_key);
                          umtxq_insert_queue(uq, UMTX_EXCLUSIVE_QUEUE);
                          umtxq_unbusy(&uq->uq_key);
  
                          error = umtxq_sleep(uq, "uwrlck", timo);
  
                          umtxq_busy(&uq->uq_key);
                          umtxq_remove_queue(uq, UMTX_EXCLUSIVE_QUEUE);
                          umtxq_unlock(&uq->uq_key);
                          if (error)
                                  break;
                          state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                  }
  
                  blocked_writers = fuword32(&rwlock->rw_blocked_writers);
                  suword32(&rwlock->rw_blocked_writers, blocked_writers-1);
                  if (blocked_writers == 1) {
                          state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
                          for (;;) {
                                  oldstate = casuword32(&rwlock->rw_state, state,
                                           state & ~URWLOCK_WRITE_WAITERS);
                                  if (oldstate == state)
                                          break;
                                  state = oldstate;
                          }
                          blocked_readers = fuword32(&rwlock->rw_blocked_readers);
                  } else
                          blocked_readers = 0;
  
                  umtxq_lock(&uq->uq_key);
                  umtxq_unbusy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
          }
  
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  static int
  do_rw_wrlock2(struct thread *td, void *obj, struct timespec *timeout)
  {
          struct timespec ts, ts2, ts3;
          struct timeval tv;
          int error;
  
          getnanouptime(&ts);
          timespecadd(&ts, timeout);
          TIMESPEC_TO_TIMEVAL(&tv, timeout);
          for (;;) {
                  error = do_rw_wrlock(td, obj, tvtohz(&tv));
                  if (error != ETIMEDOUT)
                          break;
                  getnanouptime(&ts2);
                  if (timespeccmp(&ts2, &ts, >=)) {
                          error = ETIMEDOUT;
                          break;
                  }
                  ts3 = ts;
                  timespecsub(&ts3, &ts2);
                  TIMESPEC_TO_TIMEVAL(&tv, &ts3);
          }
          if (error == ERESTART)
                  error = EINTR;
          return (error);
  }
  
  static int
  do_rw_unlock(struct thread *td, struct urwlock *rwlock)
  {
          struct umtx_q *uq;
          uint32_t flags;
          int32_t state, oldstate;
          int error, q, count;
  
          uq = td->td_umtxq;
          flags = fuword32(&rwlock->rw_flags);
          error = umtx_key_get(rwlock, TYPE_RWLOCK, GET_SHARE(flags), &uq->uq_key);
          if (error != 0)
                  return (error);
  
          state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
          if (state & URWLOCK_WRITE_OWNER) {
                  for (;;) {
                          oldstate = casuword32(&rwlock->rw_state, state, 
                                  state & ~URWLOCK_WRITE_OWNER);
                          if (oldstate != state) {
                                  state = oldstate;
                                  if (!(oldstate & URWLOCK_WRITE_OWNER)) {
                                          error = EPERM;
                                          goto out;
                                  }
                          } else
                                  break;
                  }
          } else if (URWLOCK_READER_COUNT(state) != 0) {
                  for (;;) {
                          oldstate = casuword32(&rwlock->rw_state, state,
                                  state - 1);
                          if (oldstate != state) {
                                  state = oldstate;
                                  if (URWLOCK_READER_COUNT(oldstate) == 0) {
                                          error = EPERM;
                                          goto out;
                                  }
                          }
                          else
                                  break;
                  }
          } else {
                  error = EPERM;
                  goto out;
          }
  
          count = 0;
  
          if (!(flags & URWLOCK_PREFER_READER)) {
                  if (state & URWLOCK_WRITE_WAITERS) {
                          count = 1;
                          q = UMTX_EXCLUSIVE_QUEUE;
                  } else if (state & URWLOCK_READ_WAITERS) {
                          count = INT_MAX;
                          q = UMTX_SHARED_QUEUE;
                  }
          } else {
                  if (state & URWLOCK_READ_WAITERS) {
                          count = INT_MAX;
                          q = UMTX_SHARED_QUEUE;
                  } else if (state & URWLOCK_WRITE_WAITERS) {
                          count = 1;
                          q = UMTX_EXCLUSIVE_QUEUE;
                  }
          }
  
          if (count) {
                  umtxq_lock(&uq->uq_key);
                  umtxq_busy(&uq->uq_key);
                  umtxq_signal_queue(&uq->uq_key, count, q);
                  umtxq_unbusy(&uq->uq_key);
                  umtxq_unlock(&uq->uq_key);
          }
  out:
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  static int
  do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
  {
          struct umtx_q *uq;
          struct timeval tv;
          struct timespec cts, ets, tts;
          uint32_t flags, count;
          int error;
  
          uq = td->td_umtxq;
          flags = fuword32(&sem->_flags);
          error = umtx_key_get(sem, TYPE_SEM, GET_SHARE(flags), &uq->uq_key);
          if (error != 0)
                  return (error);
          umtxq_lock(&uq->uq_key);
          umtxq_busy(&uq->uq_key);
          umtxq_insert(uq);
          umtxq_unlock(&uq->uq_key);
  
          if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0)
                  casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
  
          count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
          if (count != 0) {
                  umtxq_lock(&uq->uq_key);
                  umtxq_unbusy(&uq->uq_key);
                  umtxq_remove(uq);
                  umtxq_unlock(&uq->uq_key);
                  umtx_key_release(&uq->uq_key);
                  return (0);
          }
  
          umtxq_lock(&uq->uq_key);
          umtxq_unbusy(&uq->uq_key);
          umtxq_unlock(&uq->uq_key);
  
          umtxq_lock(&uq->uq_key);
          if (timeout == NULL) {
                  error = umtxq_sleep(uq, "usem", 0);
          } else {
                  getnanouptime(&ets);
                  timespecadd(&ets, timeout);
                  TIMESPEC_TO_TIMEVAL(&tv, timeout);
                  for (;;) {
                          error = umtxq_sleep(uq, "usem", tvtohz(&tv));
                          if (error != ETIMEDOUT)
                                  break;
                          getnanouptime(&cts);
                          if (timespeccmp(&cts, &ets, >=)) {
                                  error = ETIMEDOUT;
                                  break;
                          }
                          tts = ets;
                          timespecsub(&tts, &cts);
                          TIMESPEC_TO_TIMEVAL(&tv, &tts);
                  }
          }
  
          if ((uq->uq_flags & UQF_UMTXQ) == 0)
                  error = 0;
          else {
                  umtxq_remove(uq);
                  if (error == ERESTART)
                          error = EINTR;
          }
          umtxq_unlock(&uq->uq_key);
          umtx_key_release(&uq->uq_key);
          return (error);
  }
  
  /*
   * Signal a userland condition variable.
   */
  static int
  do_sem_wake(struct thread *td, struct _usem *sem)
  {
          struct umtx_key key;
          int error, cnt, nwake;
          uint32_t flags;
  
          flags = fuword32(&sem->_flags);
          if ((error = umtx_key_get(sem, TYPE_SEM, GET_SHARE(flags), &key)) != 0)
                  return (error); 
          umtxq_lock(&key);
          umtxq_busy(&key);
          cnt = umtxq_count(&key);
          nwake = umtxq_signal(&key, 1);
          if (cnt <= nwake) {
                  umtxq_unlock(&key);
                  error = suword32(
                      __DEVOLATILE(uint32_t *, &sem->_has_waiters), 0);
                  umtxq_lock(&key);
          }
          umtxq_unbusy(&key);
          umtxq_unlock(&key);
          umtx_key_release(&key);
          return (error);
  }
  
  int
  sys__umtx_lock(struct thread *td, struct _umtx_lock_args *uap)
      /* struct umtx *umtx */
  {
          return _do_lock_umtx(td, uap->umtx, td->td_tid, 0);
  }
  
  int
  sys__umtx_unlock(struct thread *td, struct _umtx_unlock_args *uap)
      /* struct umtx *umtx */
  {
          return do_unlock_umtx(td, uap->umtx, td->td_tid);
  }
  
  inline int
  umtx_copyin_timeout(const void *addr, struct timespec *tsp)
  {
          int error;
  
          error = copyin(addr, tsp, sizeof(struct timespec));
          if (error == 0) {
                  if (tsp->tv_sec < 0 ||
                      tsp->tv_nsec >= 1000000000 ||
                      tsp->tv_nsec < 0)
                          error = EINVAL;
          }
          return (error);
  }
  
  static int
  __umtx_op_lock_umtx(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_lock_umtx(td, uap->obj, uap->val, ts));
  }
  
  static int
  __umtx_op_unlock_umtx(struct thread *td, struct _umtx_op_args *uap)
  {
          return (do_unlock_umtx(td, uap->obj, uap->val));
  }
  
  static int
  __umtx_op_wait(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_wait(td, uap->obj, uap->val, ts, 0, 0);
  }
  
  static int
  __umtx_op_wait_uint(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_wait(td, uap->obj, uap->val, ts, 1, 0);
  }
  
  static int
  __umtx_op_wait_uint_private(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_wait(td, uap->obj, uap->val, ts, 1, 1);
  }
  
  static int
  __umtx_op_wake(struct thread *td, struct _umtx_op_args *uap)
  {
          return (kern_umtx_wake(td, uap->obj, uap->val, 0));
  }
  
  #define BATCH_SIZE      128
  static int
  __umtx_op_nwake_private(struct thread *td, struct _umtx_op_args *uap)
  {
          int count = uap->val;
          void *uaddrs[BATCH_SIZE];
          char **upp = (char **)uap->obj;
          int tocopy;
          int error = 0;
          int i, pos = 0;
  
          while (count > 0) {
                  tocopy = count;
                  if (tocopy > BATCH_SIZE)
                          tocopy = BATCH_SIZE;
                  error = copyin(upp+pos, uaddrs, tocopy * sizeof(char *));
                  if (error != 0)
                          break;
                  for (i = 0; i < tocopy; ++i)
                          kern_umtx_wake(td, uaddrs[i], INT_MAX, 1);
                  count -= tocopy;
                  pos += tocopy;
          }
          return (error);
  }
  
  static int
  __umtx_op_wake_private(struct thread *td, struct _umtx_op_args *uap)
  {
          return (kern_umtx_wake(td, uap->obj, uap->val, 1));
  }
  
  static int
  __umtx_op_lock_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_lock_umutex(td, uap->obj, ts, 0);
  }
  
  static int
  __umtx_op_trylock_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_lock_umutex(td, uap->obj, NULL, _UMUTEX_TRY);
  }
  
  static int
  __umtx_op_wait_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_lock_umutex(td, uap->obj, ts, _UMUTEX_WAIT);
  }
  
  static int
  __umtx_op_wake_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_wake_umutex(td, uap->obj);
  }
  
  static int
  __umtx_op_unlock_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_unlock_umutex(td, uap->obj);
  }
  
  static int
  __umtx_op_set_ceiling(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_set_ceiling(td, uap->obj, uap->val, uap->uaddr1);
  }
  
  static int
  __umtx_op_cv_wait(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_cv_wait(td, uap->obj, uap->uaddr1, ts, uap->val));
  }
  
  static int
  __umtx_op_cv_signal(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_cv_signal(td, uap->obj);
  }
  
  static int
  __umtx_op_cv_broadcast(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_cv_broadcast(td, uap->obj);
  }
  
  static int
  __umtx_op_rw_rdlock(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL) {
                  error = do_rw_rdlock(td, uap->obj, uap->val, 0);
          } else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  error = do_rw_rdlock2(td, uap->obj, uap->val, &timeout);
          }
          return (error);
  }
  
  static int
  __umtx_op_rw_wrlock(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL) {
                  error = do_rw_wrlock(td, uap->obj, 0);
          } else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
  
                  error = do_rw_wrlock2(td, uap->obj, &timeout);
          }
          return (error);
  }
  
  static int
  __umtx_op_rw_unlock(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_rw_unlock(td, uap->obj);
  }
  
  static int
  __umtx_op_sem_wait(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_sem_wait(td, uap->obj, ts));
  }
  
  static int
  __umtx_op_sem_wake(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_sem_wake(td, uap->obj);
  }
  
  static int
  __umtx_op_wake2_umutex(struct thread *td, struct _umtx_op_args *uap)
  {
          return do_wake2_umutex(td, uap->obj, uap->val);
  }
  
  typedef int (*_umtx_op_func)(struct thread *td, struct _umtx_op_args *uap);
  
  static _umtx_op_func op_table[] = {
          __umtx_op_lock_umtx,            /* UMTX_OP_LOCK */
          __umtx_op_unlock_umtx,          /* UMTX_OP_UNLOCK */
          __umtx_op_wait,                 /* UMTX_OP_WAIT */
          __umtx_op_wake,                 /* UMTX_OP_WAKE */
          __umtx_op_trylock_umutex,       /* UMTX_OP_MUTEX_TRYLOCK */
          __umtx_op_lock_umutex,          /* UMTX_OP_MUTEX_LOCK */
          __umtx_op_unlock_umutex,        /* UMTX_OP_MUTEX_UNLOCK */
          __umtx_op_set_ceiling,          /* UMTX_OP_SET_CEILING */
          __umtx_op_cv_wait,              /* UMTX_OP_CV_WAIT*/
          __umtx_op_cv_signal,            /* UMTX_OP_CV_SIGNAL */
          __umtx_op_cv_broadcast,         /* UMTX_OP_CV_BROADCAST */
          __umtx_op_wait_uint,            /* UMTX_OP_WAIT_UINT */
          __umtx_op_rw_rdlock,            /* UMTX_OP_RW_RDLOCK */
          __umtx_op_rw_wrlock,            /* UMTX_OP_RW_WRLOCK */
          __umtx_op_rw_unlock,            /* UMTX_OP_RW_UNLOCK */
          __umtx_op_wait_uint_private,    /* UMTX_OP_WAIT_UINT_PRIVATE */
          __umtx_op_wake_private,         /* UMTX_OP_WAKE_PRIVATE */
          __umtx_op_wait_umutex,          /* UMTX_OP_UMUTEX_WAIT */
          __umtx_op_wake_umutex,          /* UMTX_OP_UMUTEX_WAKE */
          __umtx_op_sem_wait,             /* UMTX_OP_SEM_WAIT */
          __umtx_op_sem_wake,             /* UMTX_OP_SEM_WAKE */
          __umtx_op_nwake_private,        /* UMTX_OP_NWAKE_PRIVATE */
          __umtx_op_wake2_umutex          /* UMTX_OP_UMUTEX_WAKE2 */
  };
  
  int
  sys__umtx_op(struct thread *td, struct _umtx_op_args *uap)
  {
          if ((unsigned)uap->op < UMTX_OP_MAX)
                  return (*op_table[uap->op])(td, uap);
          return (EINVAL);
  }
  
  #ifdef COMPAT_FREEBSD32
  int
  freebsd32_umtx_lock(struct thread *td, struct freebsd32_umtx_lock_args *uap)
      /* struct umtx *umtx */
  {
          return (do_lock_umtx32(td, (uint32_t *)uap->umtx, td->td_tid, NULL));
  }
  
  int
  freebsd32_umtx_unlock(struct thread *td, struct freebsd32_umtx_unlock_args *uap)
      /* struct umtx *umtx */
  {
          return (do_unlock_umtx32(td, (uint32_t *)uap->umtx, td->td_tid));
  }
  
  struct timespec32 {
          uint32_t tv_sec;
          uint32_t tv_nsec;
  };
  
  static inline int
  umtx_copyin_timeout32(void *addr, struct timespec *tsp)
  {
          struct timespec32 ts32;
          int error;
  
          error = copyin(addr, &ts32, sizeof(struct timespec32));
          if (error == 0) {
                  if (ts32.tv_sec < 0 ||
                      ts32.tv_nsec >= 1000000000 ||
                      ts32.tv_nsec < 0)
                          error = EINVAL;
                  else {
                          tsp->tv_sec = ts32.tv_sec;
                          tsp->tv_nsec = ts32.tv_nsec;
                  }
          }
          return (error);
  }
  
  static int
  __umtx_op_lock_umtx_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_lock_umtx32(td, uap->obj, uap->val, ts));
  }
  
  static int
  __umtx_op_unlock_umtx_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          return (do_unlock_umtx32(td, uap->obj, (uint32_t)uap->val));
  }
  
  static int
  __umtx_op_wait_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_wait(td, uap->obj, uap->val, ts, 1, 0);
  }
  
  static int
  __umtx_op_lock_umutex_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_lock_umutex(td, uap->obj, ts, 0);
  }
  
  static int
  __umtx_op_wait_umutex_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_lock_umutex(td, uap->obj, ts, _UMUTEX_WAIT);
  }
  
  static int
  __umtx_op_cv_wait_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_cv_wait(td, uap->obj, uap->uaddr1, ts, uap->val));
  }
  
  static int
  __umtx_op_rw_rdlock_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL) {
                  error = do_rw_rdlock(td, uap->obj, uap->val, 0);
          } else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  error = do_rw_rdlock2(td, uap->obj, uap->val, &timeout);
          }
          return (error);
  }
  
  static int
  __umtx_op_rw_wrlock_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL) {
                  error = do_rw_wrlock(td, uap->obj, 0);
          } else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
  
                  error = do_rw_wrlock2(td, uap->obj, &timeout);
          }
          return (error);
  }
  
  static int
  __umtx_op_wait_uint_private_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return do_wait(td, uap->obj, uap->val, ts, 1, 1);
  }
  
  static int
  __umtx_op_sem_wait_compat32(struct thread *td, struct _umtx_op_args *uap)
  {
          struct timespec *ts, timeout;
          int error;
  
          /* Allow a null timespec (wait forever). */
          if (uap->uaddr2 == NULL)
                  ts = NULL;
          else {
                  error = umtx_copyin_timeout32(uap->uaddr2, &timeout);
                  if (error != 0)
                          return (error);
                  ts = &timeout;
          }
          return (do_sem_wait(td, uap->obj, ts));
  }
  
  static int
  __umtx_op_nwake_private32(struct thread *td, struct _umtx_op_args *uap)
  {
          int count = uap->val;
          uint32_t uaddrs[BATCH_SIZE];
          uint32_t **upp = (uint32_t **)uap->obj;
          int tocopy;
          int error = 0;
          int i, pos = 0;
  
          while (count > 0) {
                  tocopy = count;
                  if (tocopy > BATCH_SIZE)
                          tocopy = BATCH_SIZE;
                  error = copyin(upp+pos, uaddrs, tocopy * sizeof(uint32_t));
                  if (error != 0)
                          break;
                  for (i = 0; i < tocopy; ++i)
                          kern_umtx_wake(td, (void *)(intptr_t)uaddrs[i],
                                  INT_MAX, 1);
                  count -= tocopy;
                  pos += tocopy;
          }
          return (error);
  }
  
  static _umtx_op_func op_table_compat32[] = {
          __umtx_op_lock_umtx_compat32,   /* UMTX_OP_LOCK */
          __umtx_op_unlock_umtx_compat32, /* UMTX_OP_UNLOCK */
          __umtx_op_wait_compat32,        /* UMTX_OP_WAIT */
          __umtx_op_wake,                 /* UMTX_OP_WAKE */
          __umtx_op_trylock_umutex,       /* UMTX_OP_MUTEX_LOCK */
          __umtx_op_lock_umutex_compat32, /* UMTX_OP_MUTEX_TRYLOCK */
          __umtx_op_unlock_umutex,        /* UMTX_OP_MUTEX_UNLOCK */
          __umtx_op_set_ceiling,          /* UMTX_OP_SET_CEILING */
          __umtx_op_cv_wait_compat32,     /* UMTX_OP_CV_WAIT*/
          __umtx_op_cv_signal,            /* UMTX_OP_CV_SIGNAL */
          __umtx_op_cv_broadcast,         /* UMTX_OP_CV_BROADCAST */
          __umtx_op_wait_compat32,        /* UMTX_OP_WAIT_UINT */
          __umtx_op_rw_rdlock_compat32,   /* UMTX_OP_RW_RDLOCK */
          __umtx_op_rw_wrlock_compat32,   /* UMTX_OP_RW_WRLOCK */
          __umtx_op_rw_unlock,            /* UMTX_OP_RW_UNLOCK */
          __umtx_op_wait_uint_private_compat32,   /* UMTX_OP_WAIT_UINT_PRIVATE */
          __umtx_op_wake_private,         /* UMTX_OP_WAKE_PRIVATE */
          __umtx_op_wait_umutex_compat32, /* UMTX_OP_UMUTEX_WAIT */
          __umtx_op_wake_umutex,          /* UMTX_OP_UMUTEX_WAKE */
          __umtx_op_sem_wait_compat32,    /* UMTX_OP_SEM_WAIT */
          __umtx_op_sem_wake,             /* UMTX_OP_SEM_WAKE */
          __umtx_op_nwake_private32,      /* UMTX_OP_NWAKE_PRIVATE */
          __umtx_op_wake2_umutex          /* UMTX_OP_UMUTEX_WAKE2 */
  };
  
  int
  freebsd32_umtx_op(struct thread *td, struct freebsd32_umtx_op_args *uap)
  {
          if ((unsigned)uap->op < UMTX_OP_MAX)
                  return (*op_table_compat32[uap->op])(td,
                          (struct _umtx_op_args *)uap);
          return (EINVAL);
  }
  #endif
  
  void
  umtx_thread_init(struct thread *td)
  {
          td->td_umtxq = umtxq_alloc();
          td->td_umtxq->uq_thread = td;
  }
  
  void
  umtx_thread_fini(struct thread *td)
  {
          umtxq_free(td->td_umtxq);
  }
  
  /*
   * It will be called when new thread is created, e.g fork().
   */
  void
  umtx_thread_alloc(struct thread *td)
  {
          struct umtx_q *uq;
  
          uq = td->td_umtxq;
          uq->uq_inherited_pri = PRI_MAX;
  
          KASSERT(uq->uq_flags == 0, ("uq_flags != 0"));
          KASSERT(uq->uq_thread == td, ("uq_thread != td"));
          KASSERT(uq->uq_pi_blocked == NULL, ("uq_pi_blocked != NULL"));
          KASSERT(TAILQ_EMPTY(&uq->uq_pi_contested), ("uq_pi_contested is not empty"));
  }
  
  /*
   * exec() hook.
   */
  static void
  umtx_exec_hook(void *arg __unused, struct proc *p __unused,
          struct image_params *imgp __unused)
  {
          umtx_thread_cleanup(curthread);
  }
  
  /*
   * thread_exit() hook.
   */
  void
  umtx_thread_exit(struct thread *td)
  {
          umtx_thread_cleanup(td);
  }
  
  /*
   * clean up umtx data.
   */
  static void
  umtx_thread_cleanup(struct thread *td)
  {
          struct umtx_q *uq;
          struct umtx_pi *pi;
  
          if ((uq = td->td_umtxq) == NULL)
                  return;
  
          mtx_lock_spin(&umtx_lock);
          uq->uq_inherited_pri = PRI_MAX;
          while ((pi = TAILQ_FIRST(&uq->uq_pi_contested)) != NULL) {
                  pi->pi_owner = NULL;
                  TAILQ_REMOVE(&uq->uq_pi_contested, pi, pi_link);
          }
          mtx_unlock_spin(&umtx_lock);
          thread_lock(td);
          sched_lend_user_prio(td, PRI_MAX);
          thread_unlock(td);
  }